KR20180000183A - A manufacturing method of cathode for all-solid state battery using sol-gel process and slurry-casting process - Google Patents

Abstract

The present invention relates to a method for preparing a positive electrode for a full solid battery by using a sol-gel process and a slurry casting process. More specifically, the method for preparing a positive electrode for a full solid battery can form a fine interface with a solid electrolyte layer by forming a gel layer by using the sol-gel process, forms a positive electrode slurry layer by using the slurry-casting process to form a fine interface with a gel layer for heat treatment, and forms the positive electrode slurry layer by mixing a conductive material, a polymer binder, a solid electrolyte with the positive electrode slurry used as an active material. Accordingly, the loading amount of the active material can be increased without increasing the energy concentration rate by lowering the interface resistance of the full solid battery, thereby significantly increasing the discharge capacity.

Description

Technical Field [0001] The present invention relates to a method for producing a positive electrode for a full-solid battery using a sol-gel method and a slurry casting method,

The present invention relates to a method for producing a positive electrode for a full-solid battery using a sol-gel method and a slurry casting method, and more particularly, to a method for producing a positive electrode for a solid electrolyte by forming a gel layer by a sol- Forming a positive electrode slurry layer by a slurry-casting process, and then heat-treating the electrode slurry to form an interface with the gel layer. The active material is coated with a conductive material, a polymeric binder, and a solid The present invention relates to a method of manufacturing a positive electrode for a full-solid battery, which is capable of significantly increasing the discharge capacity by increasing the loading amount of the active material while increasing the energy density by reducing the interfacial resistance of the entire solid electrolyte by mixing the electrolyte.

BACKGROUND ART [0002] Today, secondary batteries are widely used in large-sized devices such as automobiles and electric power storage systems, and small-sized devices such as mobile phones, camcorders, and notebook computers. The lithium ion battery as a secondary battery has an advantage that the energy density is higher than that of the nickel-manganese battery or the nickel-cadmium battery and the capacity per unit area is large.

However, since a lithium ion battery uses a liquid electrolyte mainly containing an organic solvent as an electrolyte, there is a high risk of leakage and fire. Therefore, all-solid state batteries with high power and high energy density and good safety have attracted attention.

All solid-state cells are batteries in which a liquid electrolyte of a lithium ion battery is replaced with a solid electrolyte. All solid-state batteries use a solid electrolyte, so there is a low risk of electrolyte leakage and fire. However, since the electrolyte for transferring lithium ions is a solid phase in all solid-state cells, it is important to uniformly mix the solid electrolyte, the conductive material and the active material to uniformly mix the ion conduction and the electron conduction path in order to improve the performance of the battery.

Particularly, the interface between the positive electrode (specifically, the positive electrode active material) and the solid electrolyte is not formed densely. The poor contact between the positive electrode and the solid electrolyte leads to an increase in the interface resistance. Therefore, the actual energy density of the entire solid-state cell becomes far less than the theoretical energy density.

Conventional pre-solid batteries are produced by using a sol-gel method or a slurry casting method on a solid electrolyte on a positive electrode. However, when manufactured by the sol-gel method, the amount of the cathode material applied is extremely limited, so it is difficult to realize a high loading anode. On the other hand, when a slurry casting method is used, a large-area anode having a high loading can be realized, but the discharge capacity is considerably low.

Korean Patent No. 10-0681455 discloses an electrode for a lithium secondary battery in which an electrode active material thick film layer is formed by applying a slurry formed by mixing a sol solution containing an electrode active material powder to a substrate, There are limitations in manufacturing the anode.

Therefore, it is necessary to research and develop a new manufacturing method which can greatly improve the battery capacity while minimizing the interface resistance between the anode and the solid electrolyte generated in the conventional all-solid-state cell.

Korean Patent No. 10-0681455

In order to solve the above problems, the anode for a full-solid battery of the present invention forms a gel layer with a sol-gel process to densely form an interface with a solid electrolyte layer, and a slurry casting method a positive electrode slurry layer is formed by a casting process and then heat treatment is performed to form an interface with the gel layer. The active material is mixed with a conductive material, a polymer binder and a solid electrolyte by a positive electrode slurry to form a positive electrode slurry layer It has been found that the discharge capacity can be greatly improved by increasing the loading amount of the active material while increasing the energy density by lowering the interfacial resistance of the entire solid battery.

Accordingly, an object of the present invention is to provide a method of manufacturing a positive electrode for a full-solid battery, which can realize a high energy density by lowering the interface resistance between the solid electrolyte and the anode.

Another object of the present invention is to provide a method for manufacturing a positive electrode for a full-solid battery, which can increase the amount of loading of the active material, thereby greatly improving the discharge capacity.

The present invention provides a process for preparing a slurry comprising: (a) preparing a buffer layer slurry comprising 5 to 20% by weight of an inorganic binder and 80 to 95% by weight of an organic solvent; (b) forming a buffer layer by applying the buffer layer slurry on the garnet solid electrolyte layer and then performing heat treatment; (c) preparing an active material precursor; (d) applying the active material precursor on the buffer layer and then drying to form a sol layer; (e) thermally treating the sol layer at 600 to 800 ° C to form a gel layer; (f) preparing a positive electrode slurry comprising 20 to 90% by weight of an active material, 1 to 20% by weight of a conductive material, 8 to 40% by weight of a solid electrolyte and 1 to 20% by weight of a polymeric binder; (g) casting the positive electrode slurry on the gel layer to form a positive electrode slurry layer; And (h) heat treating the positive electrode slurry layer.

A method for manufacturing a positive electrode for a full-solid battery according to the present invention includes forming a gel layer with a sol-gel process, forming a positive electrode slurry layer thereon by a slurry-casting process, Whereby the interface between the solid electrolyte and the anode can be densely formed.

The method of manufacturing the positive electrode slurry according to the present invention can improve the discharge capacity by increasing the loading amount of the active material by mixing the active material with the conductive material, the polymer binder and the solid electrolyte with the positive electrode slurry to form the positive electrode slurry layer.

The method for manufacturing a positive electrode for a full-solid battery according to the present invention can realize a high energy density by lowering the interface resistance between the solid electrolyte and the positive electrode, and further improve the performance of the entire solid battery.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a positive electrode for a full solid battery according to the present invention. FIG.
FIG. 2 schematically shows a structure of a pre-solid battery manufactured according to the present invention.
3 is a graph showing charge / discharge (a) and impedance (b) of the all solid-state cell manufactured in Comparative Example 1 of the present invention.
4 is a graph showing charge / discharge (a) and impedance (b) of the all solid-state cell produced in Comparative Example 2 of the present invention.
FIG. 5 is a graph of charge / discharge (a) and impedance (b) of a pre-solid battery manufactured in an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to one embodiment.

The present invention relates to a method for producing a positive electrode for a full-solid battery by forming a gel layer with a sol-gel process, forming a positive electrode slurry layer thereon by a slurry-casting process, ≪ / RTI >

Specifically, the method for producing a positive electrode for a full-solid battery of the present invention comprises the steps of: (a) preparing a buffer layer slurry containing 5 to 20% by weight of an inorganic binder and 80 to 95% by weight of an organic solvent; (b) forming a buffer layer by applying the buffer layer slurry on the garnet solid electrolyte layer and then performing heat treatment; (c) preparing an active material precursor; (d) applying the active material precursor on the buffer layer and then drying to form a sol layer; (e) thermally treating the sol layer at 600 to 800 ° C to form a gel layer; (f) preparing a positive electrode slurry comprising 20 to 90% by weight of an active material, 1 to 20% by weight of a conductive material, 8 to 40% by weight of a solid electrolyte and 1 to 20% by weight of a polymeric binder; (g) casting the positive electrode slurry on the gel layer to form a positive electrode slurry layer; And (h) heat treating the positive electrode slurry layer.

According to a preferred embodiment of the present invention, in the step (a), the buffer layer slurry contains 5 to 20% by weight of an inorganic binder and 80 to 95% by weight of an organic solvent, and lithium borate (Li ₃ BO ₃ ) May be used, and ethanol, toluene, or a mixture thereof may be used as the organic solvent. The buffer layer slurry is formed to increase the contact between the anode and the solid electrolyte to facilitate electron transfer. Particularly when the inorganic binder content is less than 5% by weight, the buffer layer formation may be insufficient. When the content is more than 20% by weight, Can be delayed.

According to a preferred embodiment of the present invention, the heat treatment in step (b) may be performed at a temperature of 650 to 750 ° C. Specifically, if the heat treatment temperature is lower than 650 ° C, crystal formation may not be performed well and electron mobility may be lowered. If the heat treatment temperature is higher than 750 ° C, electron mobility may be affected by deformation of the crystal phase.

According to a preferred embodiment of the present invention, the active material precursor in step (c) may be prepared by mixing lithium nitrate, cobalt nitrate, a polymer, and an organic solvent.

According to a preferred embodiment of the present invention, in the step (c), the precursor of the active material is selected from the group consisting of nickel nitrate, lithium nitrate, cobalt nitrate, manganese nitrate, And the like.

Here, the polymer may be mixed to form a film. As such a polymer, polyvinyl pyrrolidone (PVP) may be used. The organic solvent may be isopropyl alcohol (IPA), or may be a mixture of water and isopropyl alcohol.

According to a preferred embodiment of the present invention, the precursor of the active material prepared in the step (c) may have a solid content of 20 to 50% by weight. The active material precursor may be lithium cobalt oxide (LiCoO ₂ ) or lithium nickel cobalt manganese oxide (Li [Ni _x Co _{1 -2 x} Mn _x ] O ₂ ) which is the same as the active material contained in the positive electrode slurry , X is 0.2 to 0.9).

According to a preferred embodiment of the present invention, drying in step (d) may be performed at 100 to 150 ° C for 2 to 4 hours. At this time, the active material precursor is dried to form a sol layer. The sol layer may be in a colloidal state before being gelated.

Such a sol layer can form a dense interface with the surface of the solid electrolyte layer. If the drying temperature is lower than 100 ° C, it is difficult to form a colloidal sol layer. If the drying temperature is higher than 150 ° C, the gelation proceeds rapidly and it is difficult to form a dense interface with the solid electrolyte layer. It is preferable to dry at 115 to 125 ° C, more preferably at 120 ° C for 3 hours.

According to a preferred embodiment of the present invention, in the step (e), the gel layer may be formed by heat-treating the sol layer at 600 to 800 ° C. to gel. The gel layer can contribute to excellent interfacial formation with the solid electrolyte layer. If the annealing temperature is less than 600 ° C, the electron mobility may be lowered due to poor crystal formation. If the annealing temperature is higher than 800 ° C, the electron mobility may be affected due to the deformation of the crystal phase. Preferably, the heat treatment is carried out at 650 to 750 占 폚, more preferably at 700 占 폚.

According to a preferred embodiment of the present invention, in the step (f), the positive electrode slurry contains 20 to 90% by weight of the active material, 1 to 20% by weight of the conductive material, 8 to 40% by weight of the solid electrolyte, and 1 to 20% . If the content of the active material is less than 20 wt%, the discharge capacity may be significantly lowered. If the content of the active material is more than 90 wt%, the stability of the film may be deteriorated. Such a positive electrode slurry can greatly increase the discharge capacity by increasing the loading amount of the active material by mixing the active material with the conductive material, the solid electrolyte and the polymer binder.

According to a preferred embodiment of the present invention, in the step (f), the cathode slurry includes lithium cobalt oxide (LiCoO ₂ ) or lithium nickel cobalt manganese oxide (Li [Ni _x Co _{1 -2 x} Mn _x ] O ₂ ) (where x is 0.2 to 0.9), at least one conductive material selected from the group consisting of super-c, acetylene black and ketjen black, an oxide-based solid electrolyte Or sulfide-based solid electrolytes, polymeric binders, which are at least one selected from the group consisting of cellulose-based, fluorine-based, rubber-based and acrylate-based ones, organic solvents such as xylene, terpineol and N-methylpyrrolidone And at least one selected from the group consisting of As the polymer binder, a cellulose-based binder may be ethyl cellulose.

According to a preferred embodiment of the present invention, in the step (g), the slurry casting method may be carried out by any one method selected from the group consisting of a doctor blade method, a dip coating method, a spray coating method and a roll coating method. The positive electrode slurry layer formed in the step (g) can realize a high loading anode, can be large-sized, and can be densely formed in a solid electrolyte.

According to a preferred embodiment of the present invention, the heat treatment in step (h) may be performed at 100 to 150 ° C for 10 to 14 hours. If the heat treatment temperature is lower than 100 ° C, the solvent may not evaporate properly and the residual solvent may interfere with the electron transfer. If the heat treatment temperature is higher than 150 ° C, the binder may be damaged and the uniformity of the film may be impaired. Preferably at 130 to 140 ° C, and more preferably at 120 ° C for 12 hours.

According to a preferred embodiment of the present invention, the thickness of the buffer layer in the step (b) ranges from 20 to 1000 nm, the thickness of the gel layer in the step (e) ranges from 20 to 1000 nm, The positive electrode slurry layer may have a thickness of 1 to 200 mu m.

Therefore, in the method of manufacturing the positive electrode for a full-solid battery of the present invention, a gel layer is formed by a sol-gel process and a positive electrode slurry layer is formed thereon by a slurry-casting process The interface between the solid electrolyte and the anode can be formed densely by heat treatment.

Further, by mixing a conductive material, a polymer binder and a solid electrolyte with a positive electrode slurry to form a positive electrode slurry layer, the loading amount of the active material can be increased to greatly improve the discharge capacity.

Further, the interface resistance between the solid electrolyte and the anode can be lowered to realize a high energy density, and further, the performance of the entire solid battery can be improved.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Example

1. Buffer layer formation

15% by weight of lithium borate (Li ₃ BO ₃ ) was mixed with 85% by weight of an ethanol solution to prepare a buffer layer slurry coating solution.

Garnet-type oxide-based solid electrolyte Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) was prepared. The thickness of the solid electrolyte was 0.5 mm. The buffer layer slurry coating solution was coated on the surface of the solid electrolyte at a thickness of 0.7 mm and then heat-treated at 700 ° C for 5 hours to form a buffer layer having a thickness of 20 nm.

2. Gel layer formation

(Molar ratio) of LiNO ₃ , Co (NO ₃ ) ₂ .6H ₂ O, polyvinylpyrrolidone (PVP), isopropanol (IPA) and water at a molar ratio of 1.1: 1: 0.02: A sol solution of the cathode active material was prepared so that the solid content was 30% by weight.

Then, the cathode active material sol solution was applied on the buffer layer to a thickness of 0.7 mm and dried at 120 ° C for 3 hours to form a sol layer having a thickness of 100 nm. Then, the sol layer was heat-treated at 700 ° C for 5 hours to form a gel layer.

3. Formation of cathode active material slurry layer

LiCoO ₂ (cathode active material), super-c (conductive material) and ethyl cellulose (polymer binder) were mixed in a weight ratio of 9: 1: 1. Then, 10 ml of xylene was mixed to prepare a cathode active material slurry coating solution with a total slurry solid content of 40% by weight.

Next, the cathode active material slurry coating liquid was applied on the gel layer to a thickness of 0.7 mm, cast by a doctor blade method, and dried at room temperature for 8 hours to form a cathode active material layer having a thickness of 100 탆. Followed by heat treatment at a temperature of 120 캜 for 12 hours to prepare a positive electrode for an all solid battery. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a positive electrode for a full solid battery according to the present invention. FIG.

4. Fabrication of all-solid composite anode

An Au thin film was formed on the opposite side of the solid electrolyte on which the positive electrode was formed by a sputtering method, and a lithium negative electrode was laminated on the Au thin film.

Next, a Ni substrate was laminated on the positive electrode and the negative electrode, respectively, and then the jig cell was tightened to produce a full solid battery. FIG. 2 schematically shows a structure of a pre-solid battery manufactured according to the present invention.

Comparative Example 1

Conducted in the same manner, and as the above embodiment except for the above-described embodiment in which the oxide-based solid electrolyte of the garnet-type _{Li 7 La 3 Zr 2 O 12} (LLZ) to form a gel (gel) layer only the all-solid battery Respectively.

Comparative Example 2

Based oxide of the garnet-type in the above embodiment the solid electrolyte of Li ₇ La ₃ Zr ₂ O _12, except that the formation of the buffer layer and a gel (gel) layer only on the (LLZ), and carried out in the same manner as in Example I Solid A battery was produced.

Experimental Example

The discharge capacity and the interface resistance of the all-solid-state cell produced in the above-described Examples and Comparative Examples 1 and 2 were measured through charging / discharging and impedance analysis at a voltage of 3.0 to 4.4 V and a current of 0.5 mA . The results are shown in Figs. 3, 4 and 5.

3 is a graph showing charge / discharge (a) and impedance (b) of the all-solid-state cell manufactured in Comparative Example 1. FIG. 4 is a graph showing charge / discharge (a) and impedance (b) of the all-solid-state cell manufactured in Comparative Example 2. FIG. 5 is a graph showing charge and discharge (a) and impedance (b) of the all solid-state cell manufactured in the above embodiment.

division Comparative Example 1 Comparative Example 2 Example Configuration characteristics of anode The solid electrolyte layer / gel layer Solid electrolyte layer / buffer layer / gel layer Solid electrolyte layer / buffer layer / gel layer / positive electrode slurry layer Discharge capacity (area capacity)
(mAh (mAh / cm ² )) 0.005
(0.01 mAh / cm ² ) 0.02
(0.04 mAh / cm ²⁾ 0.034
(0.08 mAh / cm ²⁾ Internal resistance (Ωcm ² ) 2.5 x 10 ⁵ 6.25 x 10 ³ 2.75 x 10 ³

In Table 1 and FIGS. 3, 4 and 5, in Comparative Example 1 in which only a gel layer including an active material and a polymer was formed on the solid electrolyte layer, the discharge capacity was as low as about 0.005 mAh, Was found to be as high as about 2.5 x 10 < ⁵ > [Omega] cm < ^{2 &} gt ;.

In Comparative Example 2 in which a buffer layer and a gel layer were formed on the solid electrolyte layer, the discharge capacity was relatively increased and the internal resistance was somewhat reduced as compared with Comparative Example 1. However, Of the total population.

On the other hand, in the case of the embodiment in which the buffer layer / the gel layer / the positive electrode slurry layer were sequentially stacked on the solid electrolyte layer, the internal resistance was found to be significantly lower than that of Comparative Examples 1 and 2 while having the highest discharge capacity . It was found that the gel layer formed on the surface of the solid electrolyte by the sol-gel method formed the dense interface between the solid electrolyte and the anode, and the internal resistance in the cell was decreased. Also, it was confirmed that the anode slurry layer was formed by the slurry casting method, and the discharge capacity was greatly improved by increasing the loading amount of the active material.

Claims (10)

(a) preparing a buffer layer slurry comprising 5 to 20% by weight of an inorganic binder and 80 to 95% by weight of an organic solvent;
(b) forming a buffer layer by applying the buffer layer slurry on the garnet solid electrolyte layer and then performing heat treatment;
(c) preparing an active material precursor;
(d) applying the active material precursor on the buffer layer and then drying to form a sol layer;
(e) thermally treating the sol layer at 600 to 800 ° C to form a gel layer;
(f) preparing a positive electrode slurry comprising 20 to 90% by weight of an active material, 1 to 20% by weight of a conductive material, 8 to 40% by weight of a solid electrolyte and 1 to 20% by weight of a polymeric binder;
(g) casting the positive electrode slurry on the gel layer to form a positive electrode slurry layer; And
(h) heat treating the positive electrode slurry layer;
Wherein the positive electrode is a positive electrode.
The method according to claim 1,
In the step (a), the slurry of the buffer layer may comprise lithium borate (Li ₃ BO ₃ ) as an inorganic binder and ethanol, toluene, or a mixture thereof as an organic solvent. Gt;
The method according to claim 1,
Wherein the heat treatment in the step (b) is performed at a temperature of 650 to 750 ° C.
The method according to claim 1,
Wherein the active material precursor is prepared by mixing lithium nitrate, cobalt nitrate, a polymer, and an organic solvent in the step (c).
The method according to claim 1,
In the step (c), the active material precursor is prepared by mixing nickel nitrate, lithium nitrate, cobalt nitrate, manganese nitrate, polymer, and organic solvent A method for manufacturing a positive electrode for a full solid battery.
The method according to claim 1,
Wherein the drying in step (d) is performed at 100 to 150 ° C for 2 to 4 hours.
The method according to claim 1,
In the step (f), the positive electrode slurry may contain lithium cobalt oxide (LiCoO ₂ ) or lithium nickel cobalt manganese oxide (Li [Ni _x Co _{1 -2 x} Mn _x ] O ₂ ) 0.2 to 0.9),
As the conductive material, at least one selected from the group consisting of super-c, acetylene black and ketjen black,
An oxide-based solid electrolyte or a sulfide-based solid electrolyte as the solid electrolyte,
The polymer binder may be at least one selected from the group consisting of a cellulose-based, fluorine-based, rubber-based, and acrylate-
Wherein the organic solvent is at least one selected from the group consisting of xylene, terpineol and N-methylpyrrolidone.
The method according to claim 1,
Wherein the step (g) is performed by any one method selected from the group consisting of a doctor blade method, a dip coating method, a spray coating method and a roll coating method.
The method according to claim 1,
Wherein the heat treatment in step (h) is performed at 100 to 150 ° C for 10 to 14 hours.
The method according to claim 1,
In the step (b), the thickness of the buffer layer is 20 to 1000 nm, the thickness of the gel layer in the step (e) is 20 to 1000 nm, and the thickness of the positive electrode slurry layer in the step (g) 200 [mu] m.

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