KR20210065584A - One-step manufacturing method of lithium-sulfide composite electrode for all-solid-state secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a lithium sulfide composite electrode for an all-solid-state battery. The present invention can contribute to the improvement of the performance of the all-solid-state battery. The present invention includes the steps of: forming a solid electrolyte layer; forming a positive electrode layer; and forming a negative electrode layer.

Description

Manufacturing method of lithium sulfide composite electrode for all-solid-state battery using a single process

The present invention relates to a method for manufacturing a positive electrode for an all-solid-state battery, and more particularly, to a method for manufacturing a positive electrode for an all-solid-state battery including _{lithium sulfide (Li 2 S) as a positive electrode active material.}

Recently, as the demand for high-energy/high-capacity batteries increases due to the technological development and generalization of electric vehicles (EVs), high-performance portable devices, and energy storage systems (ESS), various researches on next-generation batteries are being actively conducted around the world. have.

However, recently, due to the risk of explosion and ignition of lithium secondary batteries, an issue regarding stability has been raised, which is because an organic electrolyte, which is vulnerable to evaporation, leakage, ignition, and explosion, is used in currently commercialized lithium secondary batteries.

Among studies to solve this problem, an all-solid-state lithium secondary battery in which a solid electrolyte is applied instead of a liquid electrolyte is receiving a lot of attention.

All-solid-state batteries require solid-state ion-conducting phases, electron-conducting phases, and active materials for electrode components, and unlike general electrolyte-based lithium secondary batteries, because charging and discharging of the battery proceeds through the movement of ions and electrons between the solid and the solid. Their contact area has a sensitive effect on the performance of the battery.

Taking sulfur (S) as an example as a cathode material, it is theoretically a material with a very high energy density (~1640 mAh/g), but since it is an insulating material with very low electron conductivity at room temperature, an additional conductive material is added to conduct electrons for use as an electrode. Enough passages must be provided. Due to these characteristics, the electrode manufacturing process is complex and step-by-step.

In addition, if sulfur is used as a cathode material, an anode material containing lithium is basically required. In order to achieve high capacity characteristics, the negative electrode must likewise have a high capacity. When lithium metal is applied as an anode material, since lithium metal is in the form of a foil, a solid electrolyte must be coated in a thin film form, and this manufacturing process is expensive in terms of cost and is technically very difficult because the metal must be coated with a ceramic.

Korean Patent Publication No. 10-2017-0125568 (published on: November 15, 2017) Korean Patent Publication No. 10-2016-0078021 (published on: 2016.07.04) Japanese Laid-Open Patent Publication No. 2013-157084 (published date: August 15, 2013)

The technical problem to be solved by the present invention is that an all-solid-state battery including a lithium-free anode can be implemented using lithium _{sulfide (Li 2 S) as a positive electrode active material, and conventional sulfur (S)} It is to provide a method for manufacturing a positive electrode for an all-solid-state battery more efficiently by significantly simplifying the process compared to the case of using the positive electrode active material.

In order to achieve the above technical object, the present invention includes lithium sulfide (Li ₂ S), phosphorus sulfide (P ₂ S ₅ ) and a conductive material, but _{the molar ratio of Li 2} S and P ₂ S ₅ exceeds 80: 20. A method for manufacturing a lithium sulfide composite electrode for an all-solid-state battery is proposed, including preparing a composite including _{Li 2} S, Li ₂ SP ₂ S ₅ and a conductive material by performing mechanical alloying on the mixture.

In this case, the mechanical alloying process is characterized in that it is performed by planetary ball milling, attrition milling, or shaker milling.

As described above, by the mechanical alloying process using high energy milling, lithium sulfide (Li ₂ S) powder and phosphorus sulfide (P ₂ S ₅ ) powder are pulverized and mechanically combined with each other to form lithium sulfide (Li ₂ S) and phosphorus sulfide _{A lithium sulfide-phosphorus sulfide (Li 2} SP ₂ S ₅ ) solid electrolyte is obtained in which (P ₂ S ₅ ) is alloyed in a molar ratio of 80: 20 _{, and the surplus Li 2} S that does not participate in the formation of the solid electrolyte is used as a positive electrode active material. Therefore, it is possible to manufacture a composite electrode including lithium sulfide (Li ₂ S) and a solid electrolyte (Li ₂ SP ₂ S _{5 ) in a single step process.}

Meanwhile, the conductive material may be carbon, but is not limited thereto, and any conductive material for an all-solid-state battery electrode known before the filing of the present invention may be used as a conductive material regardless of the type thereof.

In another aspect of the present invention, there is provided a method for manufacturing an all-solid-state battery comprising the method for manufacturing the lithium sulfide composite electrode, comprising the steps of: (a) forming a solid electrolyte layer by pressing _{Li 2} SP ₂ S _{5 powder;} (b) a mixed powder including lithium sulfide (Li ₂ S) powder, phosphorus sulfide (P ₂ S ₅ ) powder, and conductive material powder, but with a molar ratio of _{Li 2} S and P ₂ S _{5 exceeding 80:20 A composite powder comprising Li 2} S, Li ₂ SP ₂ S ₅ and a conductive material is prepared by performing mechanical alloying, and the composite powder is provided on one surface of the solid electrolyte layer and then pressurized to form an anode layer step; and (c) providing the anode material powder or thin film on the other surface of the solid electrolyte layer, and then pressurizing to form the anode layer.

_{According to the present invention, since lithium sulfide (Li 2} S) rather than sulfur (S) is used as the positive electrode active material, restrictions on the material of the negative electrode material are reduced, so that the negative electrode layer is formed of a lithium-free anode can be For example, an indium foil as an anode material thin film can be provided on the other surface of the solid electrolyte layer and pressurized to form an anode layer. In this way, by applying indium as an anode material, an all-solid-state battery with high capacity and excellent stability can be manufactured.

Furthermore, in another aspect of the present invention, an all-solid-state battery manufactured by the method for manufacturing an all-solid-state battery and including a lithium sulfide composite electrode as an anode is proposed.

According to the method for manufacturing a lithium sulfide composite electrode for an all-solid-state battery according to the present invention, a composite electrode is manufactured using lithium sulfide (Li ₂ S), not sulfur (S), as a positive electrode active material, but a two-step process (solid electrolyte (Li ₂ SP) ₂ S ₅ ) manufacturing step - a single-step process of simultaneously manufacturing a solid electrolyte and a composite electrode instead of the solid electrolyte-containing composite electrode manufacturing step) (Mechanical alloying is performed after mixing _{Li 2} S, P ₂ S _{5 and a conductive material)} By manufacturing a lithium sulfide composite electrode with a lithium sulfide composite electrode, the process time is shortened compared to the case of sequentially manufacturing the solid electrolyte and the composite electrode, and the morphology of the electrode material particles is improved, thereby contributing to the improvement of the performance of the all-solid-state battery. have.

In addition, according to the present invention, a lithium sulfide composite electrode can be manufactured without side reactions, and since lithium sulfide (Li ₂ S) rather than sulfur (S) is used as the positive electrode active material, restrictions on the material of the anode material are reduced, so that indium metal An all-solid-state battery can be easily manufactured by using a cathode material such as a lithium sulfide composite electrode as an anode and an all-solid-state battery having a high capacity and excellent stability by applying indium as a cathode.

1 schematically shows a lithium sulfide composite electrode manufacturing process through a single process (One-step) according to Example 1 of the present application and a lithium sulfide composite electrode manufacturing process through a multiple process (Two-step) according to Comparative Example 1 It is a drawing.
2 is a schematic diagram of a manufacturing process of an all-solid-state lithium sulfide all-solid-state battery according to Example 2 and Comparative Example 2 of the present application and a cross-sectional structure of the all-solid-state battery.
3 is a SEM-EDS of a lithium sulfide composite electrode manufactured using a single process (one-step) according to Example 1 of the present application and a lithium sulfide composite electrode manufactured through a multiple process (two-step) according to Comparative Example 1; This is the mapping result.
4 is a measurement result and cycle test result of the charge/discharge capacity of the all-solid-state battery according to Example 2 of the present application.
5 is a measurement result and cycle test results of the charge/discharge capacity of the all-solid-state battery according to Comparative Example 2.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Since the embodiment according to the concept of the present invention may have various changes and may have various forms, specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiment according to the concept of the present invention with respect to a specific disclosed form, and should be understood to include all changes, equivalents or substitutes included in the spirit and scope of the present invention.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate that the described feature, number, step, operation, component, part, or a combination thereof exists, and includes one or more other features or numbers. , it is to be understood that it does not preclude the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in detail with reference to examples.

Example

_{Li 2} S, a starting material of a glassy sulfide-based solid electrolyte, can be used as a cathode active material for a lithium secondary battery, and has a theoretical capacity of ~1164 mAh/g, which is much higher than the capacities of LCO, LMO, NMC, etc. which are commonly used today.

When Li ₂ S is applied as a positive electrode active material, it is possible to select a negative electrode material that does not contain lithium, so that the selection of the negative electrode material may be more free. In addition, as mentioned in the background art related to the present invention, the sulfur electrode is generally manufactured through several steps because it is necessary to prepare a cathode active material and an electrolyte, which are components, and it is difficult to expect optimized morphology as well as productivity. There are disadvantages. On the other hand, in the case of the all-solid battery Li ₂ S is applied to the positive electrode active material Li ₂ S may simplify the manufacturing process if good use of this point because it includes both the solid electrolyte (Li ₂ SP ₂ S ₅₎ and an anode .

Li ₂ SP ₂ S ₅ sulfide in a molar ratio in the solid electrolyte is Li ₂ S can occupy a maximum is known as the _{80 Li 2 S-20 P 2} S 5 (80:20). Based on this, a high rate of Li ₂ S than 80 mol% P ₂ S ₅ and reaction (mechanical alloying) sikindamyeon _{80 Li 2 S-20 P 2} S 5 surplus Li ₂ S solid soon as the electrolyte is prepared did not simultaneously participating in the reaction remains as a positive electrode active material, so it is possible to manufacture a composite electrode composed of lithium sulfide and a solid electrolyte in a single process. In addition, the electrolyte and active material particle size and distribution can be improved because electrolyte preparation and composite construction are performed in one process using a high-energy ball mill.

In this embodiment, as described above, the electrolyte and the composite were manufactured in one process, and as a comparative example, the electrolyte and the composite were sequentially manufactured through the conventional composite electrode manufacturing process (Two-step) to compare both. , which will be described in detail below.

<Example 1> Preparation of lithium sulfide composite electrode through one-step

80+α (Li ₂ S): 20 (P ₂ S ₅ ) mol% After carbon was added to the composite, a high energy ball milling process was performed. Finally, after the reaction, α=88.5 so that the weight ratio of the solid electrolyte (80 Li ₂ S-20 P ₂ S ₅ (mol%)): the positive electrode active material (Li ₂ S): the conductive material (carbon) is 2: 1: 1 was selected as

A zirconia ball of 5φ was placed in the milling pot at a BPR (ball to powder weight ratio) of 50:1 (wt%) and sealed in a glove box to maintain the Ar atmosphere inside the milling pot. The sealed milling pot was subjected to planetary ball milling at 370 rpm for 30 hours. A solid natural electrolyte (80 Li ₂ S-20 P ₂ S _{5 (mol%)) is produced through a single mechanical alloying process, and at the same time, Li 2} S and carbon, which do not participate in the reaction, are included as active materials and conductive materials, respectively. It is possible to manufacture a composite cathode material, and it is possible to manufacture a solid electrolyte through a high-energy ball mill process, and to evenly disperse and refine each component.

<Comparative Example 1> Manufacturing of lithium sulfide composite electrode through two-step

(80 Li ₂ S-20 P ₂ S ₅ (mol%)) For the production of solid electrolyte, Li ₂ S and P ₂ S ₅ were put in a planetary ball milling pot in a molar ratio of 80:20, and a zirconia ball of 10φ was BPR (ball to powder weight ratio) was put into 30:1 (wt%), and then sealed in a glove box to maintain the Ar atmosphere inside the milling pot. The sealed milling pot was subjected to planetary ball milling at 370 rpm for 30 hours _{to prepare a solid earth electrolyte (80 Li 2} S-20 P ₂ S ₅ (mol%)) by mechanical alloying method. Thereafter, after stopping milling, Li ₂ S and carbon are further added to form a solid electrolyte (80 Li ₂ S-20 P ₂ S ₅ (mol%)): a positive electrode active material (Li ₂ S): a conductive material (carbon). A composite having a weight ratio of 2 : 1 : 1 was constructed. A sulfide-based composite cathode material was prepared by additionally performing planetary ball milling at a speed of 370 rpm for 3 hours.

<Example 2> Preparation of an all-solid lithium sulfide cell including the lithium sulfide composite electrode prepared in Example 1 (see FIG. 2)

- 0.1 g of solid electrolyte (Li ₂ SP ₂ S ₅ ) was put into the prepared test mold and pressed under a pressure of 30 MPa to form a disc pellet.

- 0.16 g of the lithium sulfide composite electrode prepared in Example 1 was added and pressed under a pressure of 30 MPa to form a cathode layer in the form of a disc pellet for the anode layer.

- Turn the mold to the opposite side, put indium metal in the form of foil, and press it under a pressure of 30 MPa to make a cathode layer.

<Comparative Example 2> Preparation of an all-solid lithium sulfide cell including the lithium sulfide composite electrode prepared in Comparative Example 1 (see FIG. 2)

- 0.1 g of solid electrolyte (Li ₂ SP ₂ S ₅ ) was put into the prepared test mold and pressed under a pressure of 30 MPa to form a disc pellet.

- 0.16 g of the lithium sulfide composite electrode prepared in Comparative Example 1 was added and pressed under a pressure of 30 MPa to form a cathode layer in the form of a disc pellet for the anode layer.

- Turn the mold to the opposite side, put indium metal in the form of foil, and press it under a pressure of 30 MPa to make a cathode layer.

<Experimental Example> Morphology analysis of all-solid lithium sulfide composite electrode and evaluation of charge/discharge performance for all-solid lithium sulfide battery

As a result of performing SEM-EDS mapping on each of the lithium sulfide composite electrodes prepared in Example 1 and Comparative Example 1, sulfur (S), phosphorus (P), carbon ( C) It was observed that the component distribution was more uniform than in the composite electrode prepared by applying multiple processes in Comparative Example 1 ( FIG. 3 ).

In order to investigate the effect of such a component distribution difference, a charge/discharge test was performed on the all-solid lithium sulfide cells according to Example 2 and Comparative Example 2, in which each lithium sulfide composite electrode of Example 1 and Comparative Example 1 was applied as a positive electrode. Performance evaluation was performed repeatedly. As a result of testing under constant current conditions of 0.064 mA/cm ² , 0.13 mA/cm ² , and 0.26 mA/cm ² , the battery of Example 2 ( FIG. 4 ) including a composite electrode manufactured by applying a single process as a positive electrode was a plurality It was observed that the battery of Comparative Example 2 (FIG. 5) including the composite electrode manufactured by applying the process as a positive electrode realized a higher capacity and was more stable at various current densities. In particular, in the 10-cycle test, the cell according to Comparative Example 2 manufactured by multiple processes exhibited an abnormal charge/discharge curve, and after that, the test could no longer be performed. That is, it can be understood that the manufacturing process affects not only the capacity but also the lifespan.

The present invention is not limited to the above embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains will have other specific forms without changing the technical spirit or essential features of the present invention It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (6)

Mechanical alloying is performed on a mixture containing lithium sulfide (Li ₂ S), phosphorus sulfide (P ₂ S ₅ ), and a conductive material, but _{the molar ratio of Li 2} S to P ₂ S _{5 exceeds 80:20.} Li ₂ S, Li ₂ SP ₂ S ₅ And comprising the step of preparing a composite comprising a conductive material,
A method for manufacturing a lithium sulfide composite electrode for an all-solid-state battery. According to claim 1,
The all-solid-state battery lithium sulfide composite electrode manufacturing method, characterized in that the mechanical alloying is performed by planetary ball milling, attrition milling, or shaker milling. According to claim 1,
The all-solid-state battery lithium sulfide composite electrode manufacturing method, characterized in that the conductive material is carbon (carbon). (a) forming a solid electrolyte layer by pressing _{Li 2} SP ₂ S _{5 powder;}
(b) a mixed powder including lithium sulfide (Li ₂ S) powder, phosphorus sulfide (P ₂ S ₅ ) powder, and conductive material powder, but with a molar ratio of _{Li 2} S and P ₂ S _{5 exceeding 80:20 A composite powder comprising Li 2} S, Li ₂ SP ₂ S ₅ and a conductive material is prepared by performing mechanical alloying, and the composite powder is provided on one surface of the solid electrolyte layer and then pressurized to form an anode layer step; and
(c) providing an anode material powder or thin film on the other surface of the solid electrolyte layer, and then pressurizing to form an anode layer. 5. The method of claim 4,
The all-solid-state battery manufacturing method, characterized in that the anode material thin film is an indium foil (indium foil). An all-solid-state battery manufactured by the manufacturing method according to claim 4 or 5.

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