KR101586536B1 - Manufacturing method of carbon fiber sheet current collector for all solid state rechargeable thin film lithium secondary battery, and all solid state rechargeable thin film lithium secondary battery comprising carbon fiber sheet current collector - Google Patents

Abstract

The present invention relates to a method for producing a carbon fiber sheet current collector for a full solid lithium secondary battery, a cell for a full solid lithium secondary battery including a carbon fiber sheet current collector, and a whole solid lithium secondary battery including the same, And a step of drying the dispersed solution, the current collector can be manufactured by a simple method, and a very good adhesion force can be maintained with the composite electrode without using a binder.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing a carbon fiber sheet current collector for a solid state lithium secondary battery, and a method for manufacturing a carbon fiber sheet current collector for a solid state lithium secondary battery, state rechargeable thin film lithium secondary battery comprising carbon fiber sheet current collector}

The present invention relates to a method for producing a carbon fiber sheet current collector for a full solid lithium secondary battery which can be produced only by dispersion and drying of carbon fibers and can maintain a very good binding force with a composite electrode without using a binder, And more particularly, to a solid-state lithium secondary battery cell and a full-solid lithium secondary battery including the same.

Recently, as semiconductor industry has been developed and integration degree has been improved, electronic devices are gradually becoming smaller and lighter. Therefore, the current and power levels required for such a trend are increasing. In line with this trend, solid-state batteries have become practical, and thin-film lithium secondary batteries have been actively researched.

The lithium ion secondary battery composed of a non-aqueous liquid electrolyte or a polymer electrolyte is excellent in charge / discharge performance, but there is a risk of explosion and ignition of the liquid electrolyte, thus making it difficult to secure safety. In addition, the electrochemical reaction between the liquid electrolyte and the electrode and the separator is complicated and deteriorates, resulting in deterioration of performance and shortening of the lifetime. In contrast, inorganic solid electrolytes are less safe than liquid electrolytes and have low lithium ion conductivity, but are safe materials without explosion or ignition hazard.

The world has agreed to improve the energy form of automobile, which is the major cause of energy pollution and the main cause of environmental pollution, in the energy crisis problem that has emerged in recent years, and the commercialization of hybrid electric vehicle equipped with lithium secondary battery, which is an energy storage device, It has already begun and is expected to be applied to a wider range of applications in the future.

As a result, lithium secondary batteries have already been developed as ubiquitous lithium secondary batteries, as they have wider range of applications to small and medium-sized energy storage devices as well as small electronic devices. As lithium secondary batteries become larger and larger, there is no risk of explosion and ignition, and development of safe battery materials, especially electrolyte materials, is an important and indispensable technology to solve.

Various inorganic materials such as oxides, halides, and sulfides have been proposed as solid electrolyte materials. In the case of a solid lithium secondary battery using a sulfide-based solid electrolyte, a three-layered structure having a composite electrode / solid electrolyte / composite electrode or composite electrode / solid electrolyte / Li- Operation is performed through the unit cell. Cells having such a structure can be manufactured in the form of a thick film through a coating process such as bulk pelletization and slurry casting through powder lamination and molding, and thereafter, by using a mold or a roll press to increase the bonding force between solid particles, Process. After the pressure is applied, the battery characteristics are evaluated as a mold, or the compressed cells are separated and sealed and assembled into a coin cell or a pouch cell. In the case of a coin / pouch cell, a cell including a metal current collector must be fabricated during the electrode forming process or during the pressurizing process. In order to include the metal current collector in the electrode forming step, the electrode is mixed with a binder and a solvent to form a slurry, and the electrode is adhered to the current collector by a thick film process such as coating. A metal foil-shaped metal current collector such as aluminum or copper, which is usually used, can maintain the binding force with the electrodes only by using a certain amount of binder even when subjected to a surface treatment. However, in the case of a solid state lithium secondary battery, since a large amount of solid electrolyte is contained in the electrode, a small amount of binder may cause problems in lithium and electron conduction of the active material and the solid electrolyte, so that the content of the binder needs to be minimized. However, this makes the adhesion force between the electrode and the current collector more disadvantageous.

Therefore, there is a demand for a technique capable of bonding the electrode and the current collector with excellent bonding force without a binder.

Japanese Patent Application Laid-Open No. 6-140052 Japanese Patent Application Laid-Open No. 2004-348972

It is an object of the present invention to provide a method for manufacturing a carbon fiber sheet current collector for a full-bore lithium secondary battery, which can be produced only by dispersing and drying carbon fibers and can maintain a very good binding force with a composite electrode without using a binder.

Another object of the present invention is to provide a cell for a full solid lithium secondary battery comprising the carbon fiber sheet current collector.

It is still another object of the present invention to provide a pre-solid lithium secondary battery including the cell.

According to an aspect of the present invention, there is provided a method for manufacturing a current collector for a carbon fiber sheet for a rechargeable lithium battery, comprising the steps of: dispersing carbon fibers in a solution; and drying the dispersed solution to produce a carbon fiber sheet can do. Further, the method may further include pressing the carbon fiber sheet after the step of manufacturing the carbon fiber sheet.

The carbon fibers may be one or more selected from the group consisting of single wall carbon nanotubes (SWCNTs), aligned carbon nanotubes (SACNTs), multiwall carbon nanotubes (MWCNTs) and vapor grown carbon fibers (VGCFs) have.

The solution is volatilized at 23 to 26 DEG C and dried at 200 DEG C or lower, preferably distilled water, acetone, ethanol and methanol.

The drying step may include a primary drying at 90 to 120 ° C for 5 to 30 minutes; And secondary drying at 40 to 70 DEG C for 9 to 12 hours.

The pressing step may be pressurized to 0.5 to 2.5 ton / cm < 2 >.

According to another aspect of the present invention, there is provided a cell for a full-solid lithium secondary battery, comprising: a carbon fiber sheet current collector manufactured according to the manufacturing method; A composite electrode slurry provided on the top surface of the carbon fiber sheet current collector; And a solid electrolyte provided on the upper surface of the composite electrode slurry.

The composite electrode slurry may be prepared by mixing one electrolyte selected from the group consisting of Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S _3, and Al ₂ S ₅ and an active material in an amount of 60:40 to 20:80 And they may further contain a conductive agent for improving the electronic conductivity.

The active material may be one selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, and a multi-component active material Li (Co, Ni, Mn, Al) O ₂ and may also include a surface-coated active material.

The solid electrolyte is a mixture of Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ and Al ₂ S ₅ in a molar ratio of 70:30 to 80:20, followed by mechanical milling and Or may be one produced by a post heat treatment process.

In order to achieve the above-mentioned further object, the full solid lithium secondary battery of the present invention may include the cell.

The carbon fiber sheet current collector for a full solid lithium secondary battery of the present invention can be produced only by dispersion and drying of carbon fibers and can maintain a very good adhesion force with a composite electrode without using a binder. In addition, since the volume change of the composite electrode can be easily accommodated due to the excellent toughness, it is possible to suppress the peeling of the current collector during the charging / discharging process for a long time. In addition, due to the high electronic conductivity of the current collector of the present invention, the characteristics of the battery as a whole can be improved, and the current collector can be easily processed into a desired shape and size, so that the present invention can be applied to all-solid state lithium secondary batteries having various structures.

1 is a view illustrating a process of manufacturing a bulk cell including a carbon fiber sheet current collector according to an embodiment of the present invention.
2 is a view illustrating a process of manufacturing a thick-film type cell including a carbon fiber sheet current collector manufactured according to an embodiment of the present invention.
3 is a photograph of a carbon fiber sheet collector manufactured according to the production example of the present invention.
4 is a SEM photograph of a carbon fiber sheet collector manufactured according to an embodiment of the present invention.
FIG. 5 is a photograph showing the binding force between a collector and a composite electrode in a bulk cell manufactured in accordance with an embodiment of the present invention and a bulk cell manufactured in a comparative example.
FIG. 6 is a graph showing charge / discharge characteristics of a solid-state lithium secondary battery including a bulk cell manufactured according to an embodiment of the present invention.

The present invention relates to a method for producing a carbon fiber sheet current collector for a full-solid lithium secondary battery which can be produced only by dispersing and drying carbon fibers and can maintain a very good binding force with a composite electrode without using a binder, The present invention relates to a cell for a full solid lithium secondary battery, and a whole solid lithium secondary battery including the same.

Hereinafter, the present invention will be described in detail.

A method for manufacturing a current collector for a full-solid lithium secondary battery according to the present invention includes the steps of: dispersing carbon fibers in a solution; And drying the dispersed solution to prepare a carbon fiber sheet. Further, the method may further include pressing the carbon fiber sheet after the step of manufacturing the carbon fiber sheet.

First, the dispersing step disperses the bundled carbon fibers into a solution as uniformly as possible in order to control the uniform distribution and thickness of the carbon fiber sheet current collector.

The carbon fiber used for producing the carbon fiber sheet used as the current collector is not particularly limited as long as it has appropriate elasticity and strength even with carbon fiber alone and can realize a mesh-type sheet. Preferably, the carbon fiber is a single wall carbon nanotube (SWCNT) , Aligned carbon nanotubes (SACNT), multiwall carbon nanotubes (MWCNT), and vapor grown carbon fibers (VGCF). The carbon fibers are dispersed in a solution and then dried to form a sheet.

The solution is not particularly limited as long as it is a solution capable of easily dispersing the carbon fibers and controlling the drying process in a temperature range in which the carbon fibers are not damaged, but is preferably volatilized at 23 to 26 ° C, And more preferably one or more selected from the group consisting of distilled water, acetone, ethanol and methanol. Since the carbon fiber sheet affects the degree of entanglement and shrinkage of the carbon fibers depending on the drying temperature and the heating rate, it is preferable to set the drying conditions according to the solution in order to produce a uniform carbon fiber sheet.

The dispersion method is not particularly limited as far as the carbon fiber is uniformly dispersed, but preferably includes a physical dispersion method using a chemical dispersion method using a surfactant and an acid treatment, or a physical dispersion method using ultrasonic dispersion and milling.

The carbon fibers dispersed in the solution should be maintained in a dispersed state that does not float or sink due to agglomeration for 20 minutes or more, preferably 30 minutes or more, so as to maintain a sufficient dispersion state during the evaporation of the solvent. If the aggregation of carbon fibers occurs within 20 minutes, the thickness of the carbon fiber sheet becomes nonuniform, and the bonding force with the composite electrode and the electronic conductivity can be reduced.

Next, the solution in which the carbon fibers are dispersed is dried to shrink the carbon fibers during the drying process to obtain a dense sheet.

Such a drying process can be carried out primarily, but it is preferable to perform the drying process in order to obtain a more dense sheet. Specifically, the carbon fiber-dispersed solution is first dried at 90 to 120 DEG C for 5 to 30 minutes; And secondary drying at 40 to 70 DEG C for 9 to 12 hours. The primary drying is performed at a high temperature to prevent aggregation of the dispersed carbon fibers. The secondary drying is carried out at a temperature lower than that of the primary drying in order to prevent the rapid shrinkage of the carbon fiber sheet and to completely remove the remaining solution For a long time.

Next, in order to improve the durability and reduce the thickness of the dried carbon fiber sheet, the carbon fiber sheet is pressed at a pressure of 0.5 to 2.5 ton / cm 2. The carbon fiber sheet thus produced has a thickness of 1 to 150 mu m. If the thickness of the carbon fiber sheet is less than the lower limit, the strength, toughness and compactness of the sheet may be lowered. If the carbon fiber sheet is above the upper limit, it may be difficult to control the thickness of the sheet uniformly, .

The carbon fiber sheet thus produced may be cut according to the shape of the electrode to be applied.

Also, the present invention provides a cell for a full solid lithium secondary battery to which the carbon fiber sheet current collector manufactured above is applied.

A cell for a full solid lithium secondary battery according to the present invention comprises the carbon fiber sheet aggregate manufactured as described above; A composite electrode slurry provided on the top surface of the carbon fiber sheet current collector; And a solid electrolyte provided on the upper surface of the composite electrode slurry.

The carbon fiber sheet current collector according to the present invention can be combined with the composite electrode with excellent binding force without using a binder or with a minimum amount of binder, and minimization of ion and electron conductivity due to use of a conventional binder can be minimized.

The solid electrolyte is a sulfide-based solid electrolyte. One solid electrolyte selected from the group consisting of Li ₂ S, which is a mesh formula, and P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ and Al ₂ S ₅ , To 80:20, followed by synthesis and amorphization using a melt-cooling method or a mechanical milling method. In addition, a heat treatment process may be further performed to improve the conductivity.

The composite electrode slurry is prepared by mixing the sulfide-based solid electrolyte, the active material, and the conductive agent in a weight ratio of 40-80: 20-60: 0-7. In order to improve the binding force of the particles when preparing the composite electrode slurry, a binder may be added within a range that does not affect the properties. The active material is selectively used in conventional positive or negative electrode active material in accordance with the voltage and capacity of the battery, but to be implemented, preferably _{LiCoO 2, LiNiO 2, LiMn 2} O 4 and a multi-component active material, Li (Co, Ni, Mn , Al) O ₂ , and may also include a surface-coated active material. In addition, the conductive agent is used for improving the electronic conductivity, and it is preferable to use one that is advantageous for application according to electrical characteristics among ordinary conductive agents.

A method of manufacturing a cell according to the present invention will be described with reference to Figs. 1 and 2. Fig.

As shown in FIG. 1, a cell for a bulk type all solid lithium secondary battery using an electrolyte supporting layer can be manufactured by two methods.

In the method 1, the composite electrode slurry is coated on the surface of the solid electrolyte pellet support, and then the carbon fiber sheet is attached to the surface of the composite electrode slurry, and the cell is manufactured by drying and pressing. In this case, the solid electrolyte coated with the composite electrode slurry may be dried, and the carbon fiber sheet attached to the surface of the composite electrode slurry and the pressing process may be performed instead of the adhesion, drying, and pressing process steps. On the lower surface of the solid electrolyte, a metal foil such as lithium and indium may be attached as a counter electrode, or a composite electrode slurry containing a negative electrode active material may be additionally coated and dried, and the cell may be manufactured through a pressing process. Here, the composite electrode slurry of the positive electrode and the negative electrode is prepared in the form of powder which has been dried beforehand, and it can be applied to the surface of the solid electrolyte to form a composite electrode.

In the method 2, after the composite electrode slurry is coated on the surface of the carbon fiber sheet, the composite electrode slurry side can be attached to the solid electrolyte, and the cell can be manufactured by drying and pressing. In this case, the carbon fiber sheet coated with the composite electrode slurry may be dried, adhered to the solid electrolyte, and pressurized in place of the adhesion, drying and pressing process. In the same manner as in the method 1, a metal foil such as lithium and indium may be adhered to the lower surface of the solid electrolyte, or a composite electrode slurry containing the negative electrode active material may be additionally coated and dried, and the cell may be manufactured through a pressing process. Here, the composite electrode slurry of the positive electrode and the negative electrode may be prepared in a powder form previously dried and then applied to the surface of the solid electrolyte to form a composite electrode.

As shown in FIG. 2, the thick-film all-solid lithium secondary battery cell using the slurry in the previous step can be manufactured as follows. The composite electrode slurry is coated on the carbon fiber sheet surface by casting or other methods and dried, and then the solid electrolyte slurry is coated on the upper surface of the composite electrode and dried to prepare a two-layer unit cell. A metal foil such as lithium and indium may be attached to the upper surface of the solid electrolyte layer as a counter electrode, or a composite electrode slurry containing the negative electrode active material may be additionally coated and dried, and the cell may be manufactured through a pressing process.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Manufacturing Example  1-4. Carbon fiber  Sheet Whole-house  Produce

0.02 g, 0.05 g, 0.08 g and 0.1 g of a multiwalled carbon nanotube (MWCNT) having a density of 0.06 g / cm ³ were added to 25 ml of acetone, respectively, and ultrasonically dispersed for 300 minutes at an output of 300-500 W for 10 minutes Carbon nanotubes were uniformly dispersed, and the suspension was poured into a mold, followed by primary drying at 100 ° C for 20 minutes and secondary drying at 60 ° C for 12 hours using an oven to prepare a carbon fiber sheet Respectively. The dried carbon fiber sheet was pressed at 2 ton / cm 2 for 1 minute and then cut into a 16 mm circular punch for application to a 16 mm diameter coin cell.

Manufacturing Example  5. Sulfide series Solid electrolyte  Produce

The mixture of Li ₂ S and P ₂ S ₅ mixed at a composition ratio of 78:22 was placed in a zirconia milling port and subjected to mechanical milling (MM) at 520 rpm for 20 hours with 12 mm 10 mm zirconia balls to obtain amorphous solid The electrolyte was synthesized. The amorphous solid electrolyte thus synthesized was crystallized into a glass-ceramic solid electrolyte through a post-heat treatment process at 210 ° C. for 3 hours in an argon atmosphere.

Manufacturing Example  6. Composite electrode Slurry  Produce

In a glove box of argon atmosphere, a solid electrolyte having a composition of 78Li ₂ S-22P ₂ S ₅ , LiCoO _{2 as a} cathode active material, and a super P-carbon were dry blended in a mass ratio of 58.8: 39.2: 2 using a mortar bowl, For the preparation, a heptane solvent which is less reactive with the solid electrolyte was added and wet mixed for 30 minutes.

Manufacturing Comparative Example  1. Metal Whole house

Aluminum foil was used as the metal collector and commercial aluminum foil with a thickness of 15 μm was purchased.

Example  1-4. Bulk cell ( Bulk cell )

The composite electrode slurry prepared in Preparation Example 6 was coated on the carbon fiber sheet (current collector) prepared in Production Example 1-4 and dried at 130 ° C for 2 hours.

The solid electrolyte prepared in Production Example 5 was put into a molding mold, and a thin electrolyte supporting layer was formed by applying a pressure of 0.5 ton / cm < 2 >, and then a composite electrode slurry having a carbon fiber sheet current collector bonded to the surface of the electrolyte layer was attached Then, a pressure of 2 ton / cm 2 was applied. Then, indium foil was attached to the other surface of the electrolyte layer as a counter electrode, and then pressure was applied at 1 ton / cm 2 to prepare a total of four bulk cells.

Comparative Example  2.

A bulk cell was produced in the same manner as in Example 1 except that the current collector produced in Comparative Example 1 was used in place of the carbon fiber sheet current collector manufactured in Example 1 as a current collector.

Test Example  One. Carbon fiber  Sheet thickness and resistance

Table 1 below shows the thickness and DC resistance measured values of the carbon fiber sheet collector manufactured according to Production Example 1-4 of the present invention.

division Weight (g) Thickness (㎛) Resistivity (Ω · ㎛) Production Example 1 0.02 33 358 Production Example 2 0.05 43 178 Production Example 3 0.08 112 289 Production Example 4 0.1 179 295

As shown in Table 1, as the weight of the carbon fiber powder was increased, the thickness was increased. However, it was confirmed that the carbon fiber sheet made of the 0.05 g powder had the smallest specific resistance.

Test Example  2. Carbon fiber  Photos of sheets and SEM  shooting

FIG. 3 is a photograph of a current collector of a carbon fiber sheet manufactured according to Example 2 of the present invention, FIG. 4 is a SEM image of a surface and a cross section of a carbon fiber sheet current collector produced according to Manufacturing Example 2 of the present invention It's a picture.

3 and 4, the carbon fiber sheet current collector according to the present invention is in the form of a thin film and can be processed into various shapes (FIG. 3). The carbon fibers are tightly bonded to one another Dimensional network structure (Fig. 4).

Test Example  3. Whole-house  Bond strength comparison

FIG. 5 is a photograph showing the binding force between a collector and a composite electrode in a bulk cell manufactured in accordance with the second embodiment of the present invention and a bulk cell manufactured in a comparative example.

5, the three-layer unit cell was extracted from the mold after the pressing process. As a result, the metal collector of the comparative example was removed from the composite electrode, but the carbon fiber sheet current collector of Example 2 retained the bond with the composite electrode .

Test Example  4. Former solidarity The lithium secondary battery Charging and discharging  characteristic

FIG. 6 is a graph showing charge / discharge characteristics of a full solid lithium secondary battery including a bulk cell manufactured according to Example 2 of the present invention. FIG.

As shown in FIG. 6, the entire solid lithium battery having a carbon fiber sheet current collector exhibits a discharge capacity of 120 mAh / g or more at a 1/20 C-rate, a discharge capacity of 80 mAh / g, the carbon fiber sheet current collector maintained a good bonding force with the composite electrode.

On the other hand, the aluminum metal current collector was not removed and could not be combined with the composite electrode, and the battery operation was hardly performed.

Claims (13)

Dispersing the carbon fibers in a solution; And
And drying the dispersed solution to prepare a carbon fiber sheet. The method for manufacturing a current collector for a full-solid lithium secondary battery according to claim 1, The method as claimed in claim 1, further comprising a step of pressing the carbon fiber sheet after the step of manufacturing the carbon fiber sheet. The method of claim 1, wherein the carbon fibers are selected from the group consisting of single wall carbon nanotubes (SWCNTs), aligned carbon nanotubes (SACNTs), multiwall carbon nanotubes (MWCNTs) Or more of the total mass of the secondary battery. 2. The method of claim 1, wherein the solution is volatilized at 23 to 26 DEG C and dried at 200 DEG C or less. The method as claimed in claim 1, wherein the solution is at least one selected from the group consisting of distilled water, acetone, ethanol, and methanol. The method of claim 1, wherein the drying step comprises: a primary drying step at 90 to 120 ° C for 5 to 30 minutes; And drying the solution at 40 to 70 DEG C for 9 to 12 hours. ≪ RTI ID = 0.0 > 11. < / RTI > 3. The method of claim 2, wherein the pressing step is performed at a pressure of 0.5 to 2.5 ton / cm < 2 >. A carbon fiber sheet collector produced by the method of any one of claims 1 to 7;
A composite electrode slurry provided on the top surface of the carbon fiber sheet current collector and containing no binder component; And
And a solid electrolyte provided on the upper surface of the composite electrode slurry. The composite electrode slurry as set forth in claim 8, wherein the composite electrode slurry comprises a mixture of one electrolyte selected from the group consisting of Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ , and Al ₂ S ₅ , : ≪ / RTI > 40 to 20:80 by weight. The cell for a full-solid-state lithium secondary battery according to claim 9, wherein the composite electrode slurry further comprises a conductive agent. The lithium _secondary battery according to claim 9, wherein the active material is one selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and a multicomponent active material Li (Co, Ni, Mn, Al) O _2. Cell for secondary battery. The solid electrolyte according to claim 8, wherein the solid electrolyte is one selected from the group consisting of Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ and Al ₂ S ₅ in a molar ratio of 70:30 to 80:20 Wherein the total weight of the total solid lithium secondary battery is in the range of 10 to 20 wt%. A full-solid lithium secondary battery comprising the cell of Claim 8.

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