KR20180041872A - Manufacturing method of electrode active material having core-shell structure for all-solid cell - Google Patents

Abstract

The present invention relates to a method for manufacturing an electrode active material having a core-shell structure for an all-solid cell. More specifically, LiOH or Li2CO3, which is a high-resistance impurity formed by pretreating an active material, is used as a precursor. A surface-coated active material with a lithium oxide layer crystallized by performing acid and heat treatment on it is prepared. So, interface resistance between the active material and solid electrolyte can be greatly reduced. A production process can be facilitated. Process costs can be greatly reduced. Mass-production can be realized at a low cost. The method includes forming an impurity layer on the surface of an active material; converting the impurity layer into a lithium oxide layer; and crystallizing the lithium oxide layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for manufacturing an electrode active material of a core-

The present invention is all-solid battery, a core-relates to a manufacturing method of the electrode active material of the shell structure, and more particularly used and the like and formed by pre-processing the active resistance impurity LiOH or Li ₂ CO ₃ as a precursor, and the living and heat treatment , The interface resistance between the active material and the solid electrolyte is greatly reduced, the manufacturing process is easy, the process cost is greatly reduced, and the entire solid that can be mass-produced at a low cost And a method for producing an electrode active material having a core-shell structure for a battery.

Unlike a general battery using a liquid electrolyte, a pre-solid battery using a sulfide-based solid electrolyte is an important factor for controlling the interface between the electrode active material and the solid electrolyte. In the case of a battery using a liquid electrolyte, contact between the electrolyte and the electrode active material is improved by soaking of the liquid electrolyte, and the interface resistance is small because there is no reaction between the liquid electrolyte and the electrode active material.

However, in the case of a pre-solid battery using a sulfide-based solid electrolyte, a chemical reaction occurs between the two substances at the interface between the solid electrolyte and the electrode active material due to high reactivity of sulfur. As a result, an interface layer having high resistance is produced. This high-resistance interface layer interferes with the movement of lithium ions between the electrode active material and the solid electrolyte, thereby deteriorating battery performance.

Therefore, in order to realize a high-performance all-solid battery, a technique for suppressing the formation of a high-resistance interface layer between the electrode active material and the solid electrolyte is required through interfacial control.

A general interface control method of a solid electrolyte may be a method of coating an electrode active material with a material having high ionic conductivity and chemical stability. Through the coating, it is possible to prevent direct contact between the electrode active material and the solid electrolyte, thereby ensuring stable lithium ion migration while suppressing reaction between the electrode active material and the solid electrolyte.

A coating material is _{LiNbO 3, Li 4 Ti 5 O} 12, LiZrO 2, Li 2 WO 3, Li 3 PO 4 and so on, but a variety of materials, of which Li ₃ PO ₄ is attracting attention as a high chemical stability with high lithium ion conductivity . In addition, Li ₃ PO ₄ is advantageous for mass production and industry because it is inexpensive compared to other coating materials, but the conventional Li ₃ PO ₄ coating process requires high manufacturing cost due to process characteristics.

Specifically, the Li ₃ PO ₄ coating process includes a sol-gel method in which a sol solution is impregnated, a spray coating method in which a sol solution is directly sprayed, and a pulsed laser deposition (PVD) method using a thin film deposition apparatus.

The sol-gel method and the spray coating method commonly use a sol solution to carry out the coating process, but the precursor for the preparation of the sol solution is quite expensive and thus not suitable for mass-production. The PVD method requires expensive vacuum deposition equipment for coating and has a disadvantage in that it is not suitable for mass-production because the vacuum state must be maintained and the cost for maintaining vacuum is very high.

Korean Patent No. 10-1202079 discloses a method for producing a cathode active material for a core-shell lithium secondary battery by high-temperature spray drying. However, expensive precursors or deposition equipment are required for a high-temperature spray drying process, And is inadequate for the application of mass production processes.

Korean Patent No. 10-1202079

In order to solve the problems as described above, the present invention uses a precursor instead of LiOH or Li ₂ CO ₃ which is a high-resistance impurity formed by pretreating an active material, It is possible to reduce the interfacial resistance between the active material and the solid electrolyte by manufacturing the electrode-active material having the core-shell structure composed of the layer shell, and to remarkably reduce the process cost and to realize the advantage of mass production at low cost. Respectively.

Accordingly, an object of the present invention is to provide a method for manufacturing an electrode active material for a core-shell structure for a full solid battery which can be mass-produced at low cost.

The present invention provides a method of manufacturing a semiconductor device, comprising: forming an impurity layer on a surface of an active material; Reacting the active material on which the impurity layer is formed with an acid in a solvent to convert the impurity layer into a lithium oxide layer; And crystallizing the lithium oxide layer, wherein the impurity layer is made of LiOH, Li ₂ CO _3, or a mixture thereof, and the lithium oxide layer is Li ₃ PO ₄ , Li ₂ B ₄ O _7, or a mixture thereof. The present invention also provides a method of manufacturing an electrode active material for a core-shell structure for an all solid-state battery.

The electrode active material of the core-shell structure according to the present invention may be prepared by coating LiOH or Li ₂ CO ₃ , which is a high-resistance impurity existing on the surface of a conventional active material, as a precursor, By producing the active material, the interface resistance between the electrode active material and the solid electrolyte can be greatly reduced.

In addition, the electrode active material of the present invention can be easily manufactured and greatly reduce the process cost by preparing a core-shell structure electrode active material composed of a lithium oxide layer shell crystallized on the active material core surface through a simple pretreatment, acid treatment and heat treatment And can be mass-produced at low cost.

1 is a schematic view illustrating a process of manufacturing an electrode active material according to an embodiment of the present invention.
FIG. 2 is a graph showing FT-IR analysis of the electrode active material prepared in the example of the present invention.
FIG. 3 is a graph showing the results of an EIS analysis of a pre-solid battery made using the electrode active material prepared in the example of the present invention and a pre-solid battery made as a comparative example.

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

In order to solve the high cost problem of the existing process, the present invention includes a step of forming an impurity layer on the active material surface, a step of converting the surface-coated active material of the impurity layer into the lithium oxide layer by reacting with the acid, and the step of crystallizing the lithium oxide layer To a method of mass-producing an electrode active material of a core-shell structure at a minimum cost.

More specifically, the method for manufacturing an electrode active material for a core-shell structure for an all solid-state battery of the present invention includes the steps of: forming an impurity layer on a surface of an active material; Reacting the active material on which the impurity layer is formed with an acid in a solvent to convert the impurity layer into a lithium oxide layer; And crystallizing the lithium oxide layer, wherein the impurity layer is made of LiOH, Li ₂ CO _3, or a mixture thereof, and the lithium oxide layer is Li ₃ PO ₄ , Li ₂ B ₄ O _7, or a mixture thereof.

Conventionally, a metal oxide coating layer is formed after removing LiOH or Li ₂ CO ₃ , which is a high-resistance impurity on the active material surface, through a high-temperature heat treatment in order to form a metal oxide coating layer on the surface of the active material.

However, in the present invention, in order to directly use an impurity on the surface of the active material as a precursor, an active material is left in the air to form an impurity layer on the surface of the active material to form an impurity layer made of LiOH, Li ₂ CO ₃ , A surface-coated electrode active material can be produced.

According to a preferred embodiment, the moisture of the active material in the step of forming the impurity layer (H ₂ O) 0.01 ~ 0.5% by volume, oxygen (O ₂₎ 15 ~ 35% by volume and carbon dioxide (CO ₂₎ 0.01 ~ 0.5 And then allowed to stand for 12 to 24 hours under a normal atmospheric pressure in an air containing a volumetric percentage to form an impurity layer on the surface of the active material.

In the pretreatment process for forming the impurity layer in the present invention, the impurity layer can be formed by simply leaving the active material in the air for a predetermined time. Preferably, it is preferable to spread the active material widely so as to maximize the air contact area with the active material. It is preferable that the reacted air in contact with the active material is allowed to circulate without stagnation. More preferably, the air is circulated in the fume hood for a certain period of time.

Particularly, in the step of forming the impurity layer, it is important that the process is performed under the condition that the process time and moisture, oxygen and carbon dioxide in the air are contained in a specific range. An impurity layer is not uniformly formed on the entire surface of the electrode active material in an environment such as a drier room where moisture is removed as described above, or in a particularly high humidity environment due to weather or the like, so that an impurity layer of a specific thickness is formed Can not. In addition, the generation of the impurity layer may be suppressed or the impurity layer may not be uniformly grown. In the present invention, the coating thickness of the impurity layer is preferably 15 to 40 nm in thickness, considering the thickness (4 to 10 nm) of the lithium oxide layer as a final target and shrinkage of the lithium oxide layer during drying and heat treatment Do.

As described above, the oxide layer can be controlled to have a thickness of 15 to 40 nm by controlling the parameters within the process time and the air condition. If the thickness of the impurity layer is less than 15 nm, there is a problem that the thickness of the crystallized lithium oxide layer is thinner than 4 nm after the heat treatment. If the thickness is more than 40 nm, the thickness of the crystallized lithium oxide layer is less than 10 nm Can be formed thick.

In the step of forming the impurity layer, the active material is at least one selected from the group consisting of LiMO ₂ layered rock salt structure, LiM ₂ O ₄ spinel structure and LiMPO ₄ olivine structure having excellent discharge capacity characteristics, wherein M May be at least one transition metal selected from the group consisting of Co, Ni, Mn, Fe, Ti, Cr, V, Zn and Cu. Preferably it is better to use the Li (Ni Co _{0 .6 0 0 .2 .2} Mn) O ₂ as the active material.

According to a preferred embodiment of the present invention, the impurity layer may be converted into a lithium oxide layer by reacting the active material having the impurity layer formed thereon with an acid in a solvent. The lithium oxide layer may be made of Li ₃ PO ₄ , Li ₂ B ₄ O _7, or a mixture thereof, which is excellent in lithium ion conductivity.

When the temperature is lower than 70 ° C, the acid solution is not completely dried. When the temperature is higher than 100 ° C The active material due to high temperature may be damaged. At this time, the pH is preferably within a range of 0.5 to 3.

The solvent used in the step of converting into the lithium oxide layer may be a solvent capable of dissolving an acid without reacting with the active material, and a solvent having a low boiling point. Preferably, the solvent is at least one selected from the group consisting of methanol, ethanol and isopropyl alcohol.

The acid used in the step of converting into the lithium oxide layer may be phosphoric acid (H ₃ PO ₄ ), boric acid (H ₃ BO ₃ ) or a mixture thereof, but is not limited thereto. The acid may form various lithium oxide layers depending on the kind of acid selected.

As a specific example, when phosphoric acid (H ₃ PO ₄ ) is used selectively, a lithium oxide layer of Li ₃ PO ₄ can be formed. When boric acid (H ₃ BO ₃ ) is selectively used, lithium of Li ₂ B ₄ O ₇ An oxide layer may be formed, but is not limited thereto.

The acid may be mixed at a concentration of 0.02 to 0.25 M (mol / L). If the concentration of the acid is less than 0.02 mol / L, the impurity layer coated on the surface of the active material may not react completely and the impurity layer may be present. If the concentration of the acid exceeds 0.25 mol / L, the active material may be damaged.

The acid may be converted into an amorphous lithium oxide layer through an oxidation-reduction reaction with an impurity layer coated on the surface of the active material.

As a specific example, in the step of converting into the lithium oxide layer, the acid treatment can form an amorphous lithium oxide layer by the following reaction formula.

[Reaction Scheme]

_{[3LiOH + H 3 PO 4 =} Li 3 PO 4 + 3H 2 O]

[3Li ₂ CO ₃ + 2H ₃ PO ₄ = 2Li ₃ PO ₄ + 3H ₂ O + 3CO ₂ ]

The lithium oxide layer formed in the step of converting into the lithium oxide layer may control the thickness depending on the acid treatment temperature and the concentration of the acid, preferably the lithium oxide layer is surface-coated to a thickness of 10 to 30 nm have. If the thickness of the lithium oxide layer is less than 10 nm, there is a problem that the thickness of the crystallized lithium oxide layer is thinner than 4 nm after the heat treatment. If the thickness is more than 30 nm, the thickness of the crystallized lithium oxide layer May be formed thicker than 10 nm.

According to a preferred embodiment of the present invention, an electrode active material having a core-shell structure can be produced by sintering an active material having a lithium oxide layer and crystallizing the lithium oxide layer.

In the step of crystallizing the lithium oxide layer, sintering may crystallize an amorphous lithium oxide layer into a crystallized lithium oxide layer through a high-temperature sintering process. At this time, the temperature is preferably raised to 450 to 600 ° C at a temperature raising rate of 5 to 10 ° C / sec for high-temperature sintering, and then sintered for 2 to 8 hours. There is a problem that it is difficult to form a desired lithium oxide layer on the crystal phase when the temperature and time conditions are exceeded.

Also, the thickness of the crystallized lithium oxide layer can be easily controlled within a range satisfying all the sintering conditions, and preferably, the lithium oxide layer is surface-coated to a thickness of 4 to 10 nm. If the thickness of the lithium oxide layer is less than 4 nm, it is difficult to suppress the interfacial diffusion reaction between the active material and the solid electrolyte. If the thickness exceeds 10 nm, lithium ion migration between the active material and the solid electrolyte may be restricted.

Therefore, the electrode active material of the core-shell structure for the all-solid-state battery of the present invention can be obtained by removing LiOH or Li ₂ CO ₃ , which are high-resistance impurities existing on the surface of the existing active material, The interface resistance between the electrode active material and the solid electrolyte can be greatly reduced.

In addition, the electrode active material of the present invention can be easily manufactured and greatly reduce the process cost by preparing a core-shell structure electrode active material composed of a lithium oxide layer shell crystallized on the active material core surface through a simple pretreatment, acid treatment and heat treatment And can be mass-produced at low cost.

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

The electrode active material of Li (Ni Co _{0 .6 0 0 .2 .2} Mn) O ₂ 20 g prepared after the moisture (H ₂ O) 0.01 ~ 0.5% by volume, oxygen (O ₂₎ 15 ~ 35% by volume and carbon dioxide ( CO ₂ ) for 24 hours to form an impurity layer made of a mixture of LiOH and Li ₂ CO _{3 on} the surface of the electrode active material. At this time, the thickness of the impurity layer was 30 nm.

Subsequently, 20 g of the active material surface-coated with the impurity layer of the mixture of LiOH and Li ₂ CO ₃ was added to 100 ml of ethanol and reacted with 0.12 ml of 0.02 MH ₃ PO ₄ at a temperature of 80 ° C. At this time, an impurity layer of a mixture of LiOH and Li ₂ CO _{3 on} the surface of the active material was oxidized and reduced with H ₃ PO ₄ to prepare an active material surface-coated with a lithium oxide layer of amorphous Li ₃ PO ₄ having a thickness of 15 nm Respectively.

Then, an active material surface-coated with a Li ₃ PO ₄ layer was placed in an Al ₂ O ₃ crucible and sintered at 500 ° C. for 5 hours in an air atmosphere to crystallize a lithium oxide layer having a thickness of 7 nm. Thus, an active material surface-coated with the crystallized Li ₃ PO ₄ layer was obtained.

1 is a schematic view illustrating a process of manufacturing the electrode active material according to the embodiment. As shown in FIG. 1, the active material surface-coated with the crystallized Li ₃ PO ₄ layer, which is an electrode active material, was pretreated in the air for a predetermined time, 0.02 MH ₃ PO ₄ and the pretreated active material were added to the organic solvent, It shows the formation of an amorphous Li ₃ PO ₄ active material coated with the treatment. And a crystalline Li ₃ PO ₄ -coated active material is formed through a sintering process.

Experimental Example 1

The FT-IR (Fourier Transform Infrared Spectroscopy) method was used to confirm the C = O bond and the P = O bond relation before and after the acid treatment and the heat treatment for the electrode active material surface-coated with the crystalline Li ₃ PO ₄ layer prepared in the above- Analysis. The results are shown in Fig.

FIG. 2 is a graph showing FT-IR analysis of the electrode active material prepared in the above embodiment. As shown in FIG. 2, in the case of (a), the C = O bond (2360, 2339 cm ^-1 ) was confirmed in the active material pretreated for 24 hours in the air. Through this process, Li ₂ CO ₃ layer was formed on the surface of the active material by pretreatment of the active material in the air.

In addition, in the case of FIG. 2 (b), it was confirmed that the C═O bond was eliminated in the electrode active material after the acid treatment and the heat treatment, and the P═O bond (1101, 1029 cm ^-1 ) was produced. As a result, it was found that Li ₂ CO _{3, which} is an undecomposed layer formed on the surface of the active material after the acid treatment and the heat treatment, was converted into Li ₃ PO ₄ .

Experimental Example 2

In order to confirm the interfacial resistance with the solid electrolyte, an all-solid battery was fabricated by a conventional method using the electrode active material surface-coated with the crystalline Li ₃ PO ₄ layer prepared in the above example. As a comparative example, an all solid battery was fabricated by a conventional method using Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ , which is the electrode active material used in the above embodiment.

Then, all the solid-state batteries prepared in Examples and Comparative Examples were subjected to EIS (Electrochemical Impedance Spectroscopy) analysis to measure the internal resistance. The results are shown in Fig.

FIG. 3 is a graph showing the results of an EIS analysis of a pre-solid battery made using the electrode active material prepared in the above embodiment and a pre-solid battery made as a comparative example. In the graph, the width of the semicircle (Z 'axis) represents the resistance of the active material and the solid electrolyte interface. As shown in FIG. 3, it was confirmed that the embodiment in which the crystalline Li ₃ PO ₄ -coated electrode active material was applied to the all solid-state cell showed a very low interface resistance as compared with the comparative example using the conventional electrode active material

Claims (9)

Forming an impurity layer on the surface of the active material;
Reacting the active material on which the impurity layer is formed with an acid in a solvent to convert the impurity layer into a lithium oxide layer; And
Sintering an active material on which a lithium oxide layer is formed to crystallize the lithium oxide layer;
, ≪ / RTI &
Wherein the impurity layer is made of LiOH, Li ₂ CO ₃ or a mixture thereof, and the lithium oxide layer is made of Li ₃ PO ₄ , Li ₂ B ₄ O ₇ or a mixture thereof. Gt; < / RTI >
The method according to claim 1,
The impurity layer is formed in air containing 0.01 to 0.5% by volume of water (H ₂ O), 15 to 35% by volume of oxygen (O ₂ ) and 0.01 to 0.5% by volume of carbon dioxide (CO ₂ ) To form an impurity layer on the surface of the active material.
The method according to claim 1,
In the step of forming the impurity layer, the active material is at least one selected from the group consisting of LiMO ₂ , LiM ₂ O ₄ and LiMPO ₄ , where M is at least one element selected from the group consisting of Co, Ni, Mn, Fe, Ti, And Cu. The method of manufacturing an electrode active material of a core-shell structure for an all solid-state battery,
The method according to claim 1,
Wherein the impurity layer is formed to a thickness of 15 to 40 nm in the step of forming the impurity layer.
The method according to claim 1,
Wherein the solvent is at least one selected from the group consisting of methanol, ethanol and isopropyl alcohol in the conversion into the lithium oxide layer.
The method according to claim 1,
Wherein the acid is phosphoric acid (H ₃ PO ₄ ), boric acid (H ₃ BO ₃ ), or a mixture thereof, and is mixed at a concentration of 0.02 to 0.25 M in the step of converting into the lithium oxide layer. A method for manufacturing an electrode active material having a shell structure.
The method according to claim 1,
Wherein the lithium oxide layer has a thickness of 10 to 30 nm in the step of converting into the lithium oxide layer.
The method according to claim 1,
Wherein the sintering in the step of crystallizing the lithium oxide layer is performed at a temperature of 450 to 600 ° C for 2 to 8 hours.
The method according to claim 1,
Wherein the crystallized lithium oxide layer in the step of crystallizing the lithium oxide layer has a thickness of 4 to 10 nm.

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