KR102292653B1 - A method for producing sulfide-based solid electrolyte - Google Patents

Abstract

The present invention relates to a method for manufacturing a solid electrolyte for a lithium secondary battery, and more particularly, to a method for manufacturing a sulfide-based solid electrolyte for a lithium secondary battery, which has excellent high ion conductivity, excellent thermal and mechanical properties, and is easy to handle, and a solid electrolyte prepared therefrom.

Description

A method for producing a sulfide-based solid electrolyte

The present invention relates to a method for manufacturing a solid electrolyte for a lithium secondary battery, and more particularly, to a method for manufacturing a sulfide-based solid electrolyte for a lithium secondary battery that is easy to handle and has excellent high ion conductivity, thermal and mechanical properties, and a solid electrolyte prepared therefrom. .

Today, portable devices such as smart phones and tablet PCs are deeply penetrating into our daily lives and are increasingly becoming indispensable in our daily lives. It is no exaggeration to say that this is thanks to advances in all battery technology. In particular, since mass production began in 1991, lithium-ion secondary batteries have rapidly developed into main power sources with the spread of mobile devices such as mobile phones and notebook PCs, using their superiority of high energy density and output voltage as weapons.

However, the lithium ion secondary battery has a risk of explosion when the organic electrolyte used for the movement of lithium ions is overheated and overcharged, and has a property of being easily ignited in the presence of an ignition source. It has a disadvantage of lowering the performance and stability of the battery.

In order to overcome these shortcomings, research on all-solid-state secondary batteries, which uses a solid electrolyte instead of a volatile electrolyte, and dramatically reduces the risk of explosion compared to lithium-ion batteries, is active. The all-solid-state battery replaces the liquid electrolyte, which is a core technology, with a solid, so that there is no ignition or explosion caused by the decomposition reaction of the electrolyte, so stability can be greatly improved. In addition, since the all-solid-state battery can use lithium metal or a lithium alloy as an anode material, there is an advantage that energy density with respect to the mass and volume of the battery can be remarkably improved.

On the other hand, when using a solid electrolyte, there is a problem in that the performance of the battery is lowered because the ion conductivity is lower than that of the liquid electrolyte and the interface state of the electrode/electrolyte is not good.

Therefore, there is a need to improve the low ionic conductivity of the solid electrolyte and improve the interface state in contact between the solid electrolyte and the electrode material. For example, it is necessary to control a method and heat treatment to minimize pores (defect) and cracks (crack) generated in the solid electrolyte heat treatment process, which is a factor that increases the resistance at the interface. In addition, a solid electrolyte having a thickness of 200 to 400 μm is required to have sufficient mechanical strength.

As a solid electrolyte to meet these needs, there is a study on a solid electrolyte using lithium sulfide (Li2S) as a starting material. An all-solid-state lithium ion battery formed by making the battery all-solid, including a solid electrolyte using lithium sulfide as a starting material, does not use a flammable organic solvent, so the safety device can be simplified, and the manufacturing cost and productivity Not only is this excellent, but it also has a feature that high voltage can be achieved by stacking them in series within the cell. In addition, in this type of solid electrolyte, there is no movement other than Li ions, so that side reactions due to movement of anions do not occur, and improvements in safety and durability are expected.

As an example of the development of a sulfide-based solid electrolyte, a lithium ion conductive sulfide glass represented by the _{general formula Li 2} SX (where X represents _{at least one sulfide of SiS 2} , GeS ₂ , and B ₂ S _{3 ) in Patent Document 1} , a sulfide-based solid electrolyte in which a high-temperature lithium ion conductive compound composed of lithium phosphate (Li ₃ PO _{4 ) is present is disclosed.}

Patent Document 2 discloses, as a solid electrolyte material, a compound having a cubic argyrodite-type crystal structure and represented by Li _7-x PS _6-x Cl _x . In particular, in the literature, there is a problem in that sulfur is easily lost due to sulfur deficiency in the calcination step in the production of a conventional aramidite-type sulfide-based solid electrolyte. Since the partial pressure of sulfur in the vicinity of the calcined sample can be increased by this, it is disclosed that there is an advantage of preventing sulfur deficiency even at a high calcination temperature.

Patent Document 1. Japanese Patent Publication No. 3184517 Patent Document 2. Republic of Korea Patent Publication 2016-0145834

Existing sulfide-based solid electrolyte materials are prone to defects due to the loss of sulfur during heat treatment and crystallization to realize ion conduction properties. As such, when a sulfur deficiency occurs, there is a problem in that it is difficult to implement the composition characteristics desired by the inventor. Meanwhile, in order to prevent sulfur deficiency, a method for manufacturing a solid electrolyte material by encapsulating it with a quartz ampoule or the like has been proposed, but in this case mass mass production is difficult. As another method, a method of calcining while applying an inert atmosphere or hydrogen sulfide (H ₂ S) gas has been proposed, and a method for producing a solid electrolyte having a stoichiometric composition with almost no sulfur vacancies has been proposed, but such an inert atmosphere or hydrogen sulfide gas The gas utilization system has a problem in that the manufacturing process cost is increased, in particular, there is a safety problem due to hydrogen sulfide gas, and there is a problem in that post-treatment costs such as an exhaust gas neutralization process after hydrogen sulfide purging occur.

Accordingly, an object of the present invention is to provide a method for manufacturing a sulfide-based solid electrolyte without sulfur vacancies without the above problems in the preparation of a sulfide-based solid electrolyte.

In order to achieve the above object, the present invention

_{a) preparing Li 2} S, P ₂ S ₅ and LiX (X is Cl, F , Br or I) as raw materials for preparing a solid electrolyte

b) mechanically mixing the raw materials; and

c) heat treatment and crystallization,

Provided is a method for manufacturing a sulfide-based solid electrolyte, wherein the heat treatment and crystallization step is performed in a state in which at least one selected from the group consisting _{of Li 2} S and P ₂ S _{5 is additionally added.}

The present invention provides a sulfide-based solid electrolyte prepared by the above method.

The present invention provides a lithium secondary battery including the sulfide-based solid electrolyte.

The present invention has the effect of preventing sulfur deficiency and providing a solid electrolyte with improved ionic conductivity by adding a small amount _{of Li 2} S and/or P ₂ S ₅ as a sulfur source in the crystallization step in the preparation of a sulfide-based solid electrolyte. Since the present invention can prevent sulfur deficiency without the use of hydrogen sulfide gas, the use of toxic gas can be avoided, and post-treatment costs such as exhaust gas neutralization process generated when hydrogen sulfide gas is used are reduced.

The present invention has the effect of providing a solid electrolyte having a desired stoichiometric composition. The sulfide-based solid electrolyte of the present invention can be used in a lithium secondary battery.

1 is XRD data of the solid electrolyte prepared in Example 1. FIG.
FIG. 2 is XRD data of the solid electrolyte prepared in Comparative Example 1. FIG.
3 is a graph measuring the LIC of the solid electrolyte prepared in Example 1.
4 is a graph measuring the LIC of the solid electrolyte prepared in Comparative Example 1.
5 is a result of measuring symmetric cell data of the solid electrolyte prepared in Example 1.
6 is a result of measuring symmetric cell data of the solid electrolyte prepared in Comparative Example 1.
7 is cell data of the solid electrolyte prepared in Example 1.
8 is cell data of the solid electrolyte prepared in Comparative Example 1.
9 is a schematic diagram of a lithium secondary battery including the solid electrolyte of the present invention.

Hereinafter, the present invention will be described in detail. The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concepts of the terms to best describe his invention. Based on the principle, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

the present invention

_{a) preparing Li 2} S, P ₂ S ₅ and LiX (X is Cl, F , Br or I) as raw materials for preparing a solid electrolyte

b) mechanically mixing the raw materials; and

c) heat treatment and crystallization,

Provided is a method for manufacturing a sulfide-based solid electrolyte, wherein the heat treatment and crystallization step is performed in a state in which at least one selected from the group consisting _{of Li 2} S and P ₂ S _{5 is additionally added.}

The present invention is for recognizing and compensating for the problem that sulfur deficiency occurs during heat treatment and crystallization after mechanical mixing of raw materials in the manufacture of a sulfide-based solid electrolyte, and to compensate for sulfur deficiency in the heat treatment and crystallization step _{Li 2} S, P ₂ S _5, etc., which are one of the main components of the solid electrolyte, are added in small amounts. Therefore, the present invention minimizes sulfur loss, so that a solid electrolyte having a composition desired by the inventor can be manufactured and its properties can be easily realized.

In the present invention, the addition amount of at least one selected from the group consisting _{of Li 2} S and P ₂ S ₅ in the heat treatment and crystallization step is preferably based on the total weight _{of Li 2} S, P ₂ S _{5 and LiX, which are raw materials for preparing a solid electrolyte.} It may be 0.01 to 1 wt%, more preferably 0.05 to 0.5 wt%.

When _{the addition amount of Li 2} S and/or P ₂ S ₅ is as described above, sulfur loss during heat treatment can be prevented and a solid electrolyte having a desired composition can be obtained.

The sulfide-based solid electrolyte of the present invention is a sulfide-based solid electrolyte having a cubic Argyrodite-type crystal structure and containing a compound represented by _{Li 7-x-2y} PS _6-xy Cl _{x as a compositional formula.} In the composition formula, x representing the content of Cl element is preferably 0.8 to 1.7. When x is 0.8 to 1.7, it is possible to form a cubic Argyrodite type, and the conductivity of lithium ions can be improved. y is a value indicating relatively how small the Li2S component is with respect to the stoichiometric composition, and it is preferable to satisfy 0<y≤-0.25x+0.5.

Hereinafter, the manufacturing method of the present invention will be described in detail.

The present invention includes the steps of preparing Li ₂ S powder, P ₂ S ₅ powder, and LiX (X is Cl, F , Br or I) powder as raw materials for preparing a solid electrolyte. The Li ₂ S, P ₂ S ₅ and LiX are Li ₂ S 35 to 45wt%, P ₂ S ₅ 35 to 45wt% and LiX 10 to 30wt% are preferably mixed, Li ₂ S 40wt%, P ₂ S ₅ 40wt%, LiX 20wt% is more preferably mixed. When Li ₂ S, P ₂ S ₅ and LiX are included in the above content, it is possible to form a cubic Argyrodite type, and it is possible to increase the conductivity of lithium ions.

In the present invention, the lithium sulfide (Li ₂ S) powder, the phosphorus sulfide (P ₂ S ₅ ) powder and the lithium chloride (LiCl) powder are preferably ground and mixed using a ball mill, a bead mill, a homogenizer, or the like. At this time, it is preferable to grind and mix enough to maintain the crystallinity of the raw material powder.

_{The present invention provides a sulfide-based composition (argyrodite / Li 2} SP ₂ S ₅ -LiCl) commonly known when mixing solid electrolyte raw materials Li ₂ S, P ₂ S ₅ and LiX (X is Cl, F , Br or I) _{In contrast, Li 2} S, which is a major component, may be added in excess. By adding Li ₂ S in an excess of 0.1 to 1.0 wt% relative to the stoichiometric content, it is possible to reduce the loss of sulfur in the subsequent heat treatment and crystallization steps. That is, Li ₂ S 35.1 to 46 wt%, P ₂ S ₅ 35 to 45 wt%, and LiX 10 to 30 wt% may be mixed.

The present invention may further include the step of primary classification before the heat treatment step after the mechanical synthesis step. The ion conductivity and crystallinity of the sulfide-based solid electrolyte can be improved by increasing the uniformity and reactivity of the powder injected during heat treatment by primary classification.

Next, the method for preparing a solid electrolyte of the present invention includes heat treatment and crystallization by adding at least one selected from the group consisting _{of Li 2} S and P ₂ S _{5 .}

The heat treatment temperature is preferably 400 to 600°C, more preferably 450°C to 550°C, and particularly preferably 480°C to 530°C.

The heat treatment time is preferably 5 to 20 hours, particularly preferably 10 to 15 hours.

In the present invention, an optimal solid electrolyte can be obtained by preferably using a glass container having no side reaction with the sulfide powder and blocking the inflow of external moisture and oxygen during heat treatment.

In addition, the present invention may further include the step of secondary classification after the step of heat treatment and crystallization.

_{In the present invention, in addition to the addition of Li 2} S and/or P ₂ S ₅ in the heat treatment and crystallization step, an additive for improving performance may be added. The additive preferably includes, but is not limited to, LiCl, LiBr, LiI, Na ₂ S, and the like.

The present invention can provide a solid electrolyte with greatly improved ion conductivity, crystallinity, cell characteristics, electrochemical stability, etc. compared to a general composition by adding _{Li 2} S and/or P ₂ S ₅ in the heat treatment and crystallization step. In addition, since the use of an inert atmosphere and hydrogen sulfide gas is unnecessary, it is effective in reducing manufacturing process cost, reducing equipment cost, and improving safety.

The present invention provides a sulfide-based solid electrolyte prepared by the above method.

the present invention

_{a) preparing Li 2} S, P ₂ S ₅ and LiX (X is Cl, F , Br or I) as raw materials for preparing a solid electrolyte

b) mechanically mixing the raw materials; and

c) heat treatment and crystallization,

The desired stoichiometric composition can be obtained by producing a sulfide-based solid electrolyte manufacturing method, wherein the heat treatment and crystallization step is _{performed in a state in which at least one selected from the group consisting of Li 2} S and P ₂ S _{5 is additionally added.} A solid electrolyte having

The present invention may _{provide a solid electrolyte in which Li 2} S, P ₂ S ₅ and LiX are _{mixed in a ratio of Li 2} S 35 to 45 wt%, P ₂ S ₅ 35 to 45 wt%, and LiX 10 to 30 wt%.

In addition, the present invention may _{provide a solid electrolyte in which the Li 2} S, P ₂ S ₅ and LiX are _{mixed in a ratio of Li 2} S 35.1 to 46 wt%, P ₂ S ₅ 35 to 45 wt%, and LiX 10 to 30 wt%.

The present invention provides a lithium secondary battery including the sulfide-based solid electrolyte.

Hereinafter, the present invention will be described in detail through an embodiment. However, the present invention is not limited to the following examples.

Example 1. Preparation of sulfide-based solid electrolyte 1

1) A generally known sulfide composition (argyrodite / Li ₂ SP ₂ S ₅ -LiCl) Li ₂ S 40wt%, P ₂ S ₅ 40wt%, and LiX 20wt% were weighed with an electronic balance, and the raw material batch was performed.

2) For uniform mixing, a batch of raw materials and a Zr ball were put into a container at a ratio of 5:1, and mechanical synthesis was performed under the conditions of 300rpm and 10 hours.

3) After mechanical synthesis, the Zr ball was separated from the composition and sieved to prepare a uniform mixture without agglomeration.

_{4) Li 2} S to Li ₂ S, P ₂ S ₅ , and to compensate for sulfur loss in the uniformly mixed composition before crystallization 0.5wt% of the total weight of LiCl was additionally added.

4) _{Li 2} S, P ₂ S _{5 to which the Li 2} S is additionally added, and A solid electrolyte was prepared after the LiCl mixture was treated in a heat treatment furnace at a crystallization temperature of 500 degrees and a crystallization retention time of 12 hours.

Example 2. Preparation of sulfide-based solid electrolyte 2

A solid electrolyte was prepared in the same manner as in Example 1, except that 0.5 wt% _{of P 2} S ₅ was added instead of adding 0.5 wt% of _{Li 2 S.}

Comparative Example 1. Preparation of sulfide crab solid electrolyte 3

A solid electrolyte was prepared in the same manner as in Example 1 except that _{Li 2} S and P ₂ S _{5 were not added.}

Experimental Example 1. XRD of solid electrolyte

XRD of the solid electrolytes prepared in Example 1 and Comparative Example 1 were measured, and the results are shown in FIGS. 1 and 2 , respectively.

According to the XRD data, it can be seen that the solid electrolyte of Example 1 of the present invention has better crystallinity and less sulfur loss than the solid electrolyte of Comparative Example 1. When high energy such as mechanical synthesis is applied after mixing conventional raw materials, it becomes a non-stoichiometric composition and has a structure with low crystallinity. There was a problem in that it is easy to generate sulfur vacancies due to this omission, making it difficult to control the desired composition. On the other hand, in the present invention, a solid electrolyte having excellent crystallinity can be prepared by maintaining a stoichiometric composition and compensating for a sulfur deficiency by additionally adding a sulfur component (LiS) lost before crystallization.

Experimental Example 2. Li ion conductivity of solid electrolyte

The ionic conductivity of the solid electrolytes prepared in Example 1 and Comparative Example 1 was measured, and the results are shown in FIGS. 3 and 4 , respectively.

It can be seen that the ionic conductivity of the solid electrolyte of Example 1 of the present invention is 4.03x10 ^{-3 S/cm, which is greater than 3.13x10 -3} S/cm, which is the ionic conductivity value of the solid electrolyte of Comparative Example 1 without compensating for sulfur loss. . That is, high crystallinity can be exhibited by having a stoichiometric structure by compensating for sulfur vacancies, and it can be seen that high ionic conductivity is realized.

Experimental Example 3. Symmetric cell data of solid electrolyte

The symmetric cell data of the solid electrolytes prepared in Example 1 and Comparative Example 1 were measured, and the results are shown in FIGS. 5 and 6 , respectively. It can be seen that Example 1 has excellent electrochemical stability because it has high crystallinity and structural stability.

Experimental Example 4. Cell data of solid electrolyte

Cell data of the solid electrolyte prepared in Example 1 and Comparative Example 1 were measured, and the results are shown in FIGS. 7 and 8, respectively.

Example 3. Preparation of secondary battery

A lithium secondary battery was prepared with the composition shown in Table 1 below and its performance was tested. A schematic diagram of a lithium secondary battery is shown in FIG. 9 .

Composite cathode
(15mg) LCO
(LiNbO3 coating) solid electrolyte
(Sulphide-based solid electrolyte) AB (conductive)
(acetylene black) 60wt% 36wt% 4 wt% solid electrolyte
(150mg) Sulfide-based solid electrolyte of Example 1 of the present invention anode
(24mg) Li foil

The test conditions are as follows.

- Current: 65.25㎂

- C-rate: 0.05C

- Cut-off voltage : 3~4.2V

- Cell dimension: 1.327cm ²

- Operating temperature : R.T

Claims (7)

_{a) preparing Li 2} S, P ₂ S ₅ and LiX (X is Cl, F , Br or I) as raw materials for preparing a solid electrolyte
b) mechanically mixing the raw materials; and
c) heat treatment and crystallization,
A method for producing a sulfide-based solid electrolyte, wherein the heat treatment and crystallization step is performed without the use of hydrogen sulfide gas by additionally adding at least one selected from the group consisting _{of Li 2} S and P ₂ S _{5 ,}
The Li ₂ S and 0.1 ~ 1wt% additional amount on one member selected from the group consisting of P ₂ S ₅ is compared to the total weight of the solid electrolyte prepared raw material Li ₂ S, P ₂ S _5, and LiX, and
The heat treatment temperature is a sulfide-based solid electrolyte manufacturing method of a cubic argyrodite (Argyrodite) type crystal structure, characterized in that 480-530 ℃ delete The method according to claim 1, wherein the heat treatment and crystallization step is performed by adding _{LiCl, LiBr, LiI or Na 2 S.} The cubic baby according to claim 1, wherein Li ₂ S, P ₂ S ₅ and LiX are _{mixed in a proportion of Li 2} S 35-46 wt%, P ₂ S ₅ 35-45 wt%, and LiX 10-30 wt%. A method of manufacturing a sulfide-based solid electrolyte having an Argyrodite-type crystal structure. _{a) preparing Li 2} S, P ₂ S ₅ and LiX (X is Cl, F , Br or I) as raw materials for preparing a solid electrolyte
b) mechanically mixing the raw materials; and
c) heat treatment and crystallization,
The heat treatment and crystallization step is performed without the use of hydrogen sulfide gas by additionally adding at least one selected from the group consisting _{of Li 2} S and P ₂ S _{5 and}
Li ₂ S, P ₂ S ₅ and LiX are _{mixed in a proportion of Li 2} S 35-46 wt%, P ₂ S ₅ 35-45 wt% and LiX 10-30 wt%,
Additional amount on one member selected from the group consisting of Li ₂ S and P ₂ S ₅ is Li ₂ S, a solid electrolyte prepared material P ₂ S _5, and is 0.1 ~ 1wt%, based on the weight of the total of LiX
The heat treatment temperature is a sulfide-based solid electrolyte having a cubic argyrodite-type crystal structure manufactured by a method characterized in that it is 480-530°C and having a stoichiometric composition. delete Lithium secondary battery comprising the sulfide-based solid electrolyte of claim 5

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