KR20220115892A - Solid Electrolyte with Li Containing Interlayer and All-Solid-State Battery comprising The Same - Google Patents

Abstract

An all-solid-state lithium secondary battery including a solid electrolyte having good interfacial properties and a manufacturing method thereof are disclosed. The present invention provides an all-solid-state lithium secondary battery including a positive electrode, a solid electrolyte separator containing lithium, and a negative electrode, wherein an interlayer of a material different from that of the solid electrolyte separator is formed on at least one surface of the solid electrolyte separator. According to the present invention, provided is an all-solid-state secondary battery capable of suppressing an increase in resistance at an interface according to repeated charging and discharging cycles even in a state that no compressive stress is applied.

Description

{Solid Electrolyte with Li Containing Interlayer and All-Solid-State Battery comprising The Same}

The present invention relates to a lithium secondary battery, and more particularly, to an all-solid lithium secondary battery including a solid electrolyte and a method for manufacturing the same.

A lithium secondary battery is largely composed of a positive electrode, an electrolyte, and a negative electrode. A commonly commercialized lithium secondary battery has a structure in which a polymer separator with a thickness of 15 to 25 μm is added in a liquid electrolyte composed of an organic solvent ^and lithium salt. The generated electrons also move from the cathode to the anode, and vice versa during charging. The driving force of such Li ⁺ ion migration is generated by chemical stability according to the potential difference between the two electrodes. The capacity (Ah) of a battery is determined by the amount of Li ⁺ ions moving from the negative electrode to the positive electrode and from the positive electrode to the negative electrode. On the other hand, since the movement of Li ⁺ ions is made through the electrolyte, the Li ⁺ ion conductivity of the electrolyte affects the charge/discharge rate of the battery.

An all-solid-state battery refers to a liquid electrolyte replaced with a solid electrolyte among the above battery components. Compared to liquid electrolytes, all-solid-state secondary batteries are attracting attention as next-generation secondary batteries because they do not have the risk of explosion or fire, simplify the manufacturing process, and increase energy density. However, while the all-solid-state secondary battery has higher safety and the like compared to liquid electrolytes, there is a problem in that the ion conductivity decreases because there are few ion conduction paths due to a decrease in interfacial contact with the electrode.

In order to solve the interfacial contact resistance problem, a hybrid electrolyte matrix of a semi-solid state introduced with a liquid electrolyte is conventionally applied. In this case, it is fundamentally difficult to secure thermal stability, and on the other hand, active material and solid A method of coating an artificial SEI layer on the surface of an active material in order to suppress a rise in resistance due to unwanted side reactions at the electrolyte interface has been proposed, but this is due to the interlayer having a relatively low ionic conductivity. Since the ionic conductivity of the active material itself was lowered, it could not be an appropriate solution.

In addition, all-solid-state secondary batteries apply or maintain a compressive stress of 5 ton/cm ² or more during electrode manufacturing or cell manufacturing in order to minimize the electrochemical reaction resistance that occurs at the interface between the electrolyte and the electrode and at the interface between the separator and the electrode. processing is required. However, the necessity of applying such compressive stress is an obstacle to the commercialization of all-solid-state batteries.

In order to solve the problems of the prior art, an object of the present invention is to provide an all-solid-state secondary battery capable of suppressing an increase in resistance at an interface.

Another object of the present invention is to provide an all-solid-state secondary battery capable of suppressing an increase in interfacial resistance due to repetition of a charge/discharge cycle even in a state where compressive stress is not applied.

Another object of the present invention is to provide a method for manufacturing the above-described lithium secondary battery.

In order to achieve the above technical object, the present invention provides an all-solid-state Li secondary battery including a positive electrode, a Li-containing solid electrolyte separator and a negative electrode, wherein at least one surface of the solid electrolyte separator is made of a material different from the solid electrolyte separator. It provides an all-solid-state Li secondary battery, characterized in that the interlayer is formed.

In the present invention, the interlayer film may be formed of a material containing at least one element selected from the group consisting of Au, Al, Sn, C, P, and graphene.

In addition, the interlayer may include a reaction product with Li contained in the solid electrolyte.

In the present invention, the interlayer film preferably has a thickness of less than 1 μm.

In order to achieve the above another technical problem, the present invention provides a method for manufacturing an all-solid Li secondary battery including a positive electrode, a solid electrolyte separator containing Li, and a negative electrode, wherein the solid electrolyte separator is provided on at least one surface of the solid electrolyte separator and forming an interlayer film of different materials; And it provides a method of manufacturing an all-solid-state Li secondary battery comprising the step of laminating the solid electrolyte separator formed with the interlayer with the positive electrode and the negative electrode. At this time, the lamination step is performed in a non-pressurized state.

In addition, the interlayer forming step may include dispersing at least one material selected from the group consisting of C, P and graphene in a solvent to prepare a slurry; applying the slurry to at least one surface of the solid electrolyte separator; and drying the applied slurry.

Alternatively, the forming of the interlayer may include depositing at least one material selected from the group consisting of Au, Al and Sn on at least one surface of the solid electrolyte separator.

Advantageous Effects of Invention According to the present invention, it is possible to provide an all-solid-state secondary battery capable of suppressing an increase in resistance at an interface according to repetition of a charge/discharge cycle even in a state where compressive stress is not applied.

1 is a diagram schematically illustrating a structure of a secondary battery according to a preferred embodiment of the present invention.
2 (a) and (b) are graphs showing the measurement results of the charging and discharging characteristics of the LPSI electrolyte and the LPSCl electrolyte cell in the present experimental example, respectively.
3 (a) and (b) are graphs showing the measurement results of the charging and discharging characteristics of the LPSI electrolyte and the LPSCl electrolyte cell in the present experimental example, respectively.
4 is a graph showing the charging and discharging characteristics of a cell manufactured according to an embodiment of the present invention.
5 is a graph showing charge/discharge characteristics of a cell manufactured according to another embodiment of the present invention.
6 is a graph showing charge/discharge characteristics of a cell manufactured according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the drawings.

1 is a diagram schematically illustrating a structure of a secondary battery according to a preferred embodiment of the present invention.

Referring to FIG. 1 , the secondary battery is interposed between the positive electrode 110 , the negative electrode 120 , the solid electrolyte 130 and the positive electrode 110 and the negative electrode 120 , and is coated on the surface of the solid electrolyte 130 . Interlayers 150A and 150B are included.

In the present invention, the positive electrode 110 includes a positive electrode active material.

In the present invention, various materials that reversibly occlude and release lithium ions may be used as the cathode active material. For example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Formula Li _{1 + y} Mn _{2 -y} O ₄ (where _y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Formula LiMn _{2 - y} MyO ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 - 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, lithium manganese composite oxide represented by Cu or Zn; disulfide compounds; Although Fe2 _{(MoO4)3 etc. are} mentioned, It is not limited only to these.

Meanwhile, in the present invention, the negative electrode 120 includes an anode active material. Carbon material, lithium metal, silicon, tin, or an alloy of these metals may be used as the negative active material.

In the present invention, the positive electrode 110 and the negative electrode 120 may further include a conductive material and a binder in addition to the active material.

On the other hand, as the solid electrolyte, it is preferable to use a material having low electron conductivity and high lithium ion conductivity. An oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a mixture thereof may be used.

Examples of the oxide-based solid electrolyte include lithium silicate (Li _3.5 Si _0.5 P _{0.5 O 4} ) _, lithium titanium phosphate (LiTi ₂ (PO ₄ ) ₂ ), _and lithium germanium phosphate ( _{LiGe 2 (} PO) ₄ ) at least one selected from the group consisting of ₃ ), Li ₂ O-SiO ₂ , Li ₂ OV ₂ O ₅ -SiO ₂ , Li ₂ OP ₂ O ₅ -B ₂ O ₃ and Li ₂ O-GeO ₂ material may be used. Moreover, you may use _the material which added _a different element, _Li3PO4 , _LiPO3 , _Li4SiO4 , _{Li2SiO3 ,} or _LiBO2 to these materials.

In addition, the sulfide-based solid electrolyte may include a sulfide such as Li ₂ SP ₂ S ₅ , SiS ₂ , GeS ₂ or B ₂ S ₃ . In addition, as the solid electrolyte, Li ₂ SP ₂ S ₅ , SiS ₂ , GeS ₂ , B ₂ S ₃ , Li ₃ PO ₄ , halogen or a halogen compound added to an inorganic solid electrolyte obtained from a mixture thereof may be used. can For example, Li-PS, Li-Ga-PS, Li-PSI, Li-PS-Cl, Li-PS-Br, Li-La-Zr-O, Li-Al-Ti-P, etc. may be used.

In the present invention, as the solid electrolyte, various forms such as crystalline or amorphous may be used. In addition, the solid electrolyte may be a mixture of a polymer in the above-described solid electrolyte. Polyamide-imide (PAI), polyimide (PI), polyamide (PA), polyamic acid, polyethylene oxide (PEO), PEPMNB (poly ( ethylene-co-propylene-co-5-methylene-2-norbornene)), polyvinylidene fluoride (PVDF), PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene), NBR (nitrile-butadiene rubber) ), PS-NBR (polystyrene nitrile-butadiene rubber), and PMMA-NBR (poly(methacrylate)nitrile-butadiene rubber) may be composed of at least one polymer selected from the group consisting of or a mixture thereof.

At this time, the ratio of solid electrolyte and polymer is solid electrolyte: polymer = 80 to 99: 1 to 20 weight ratio by dissolving the polymer in a solvent such as heptane and mixing it with solid electrolyte powder to prepare a slurry, then doctor blade A solid electrolyte layer can be prepared by a coating method using

Meanwhile, in the present invention, the interlayers 150A and 150B reduce the interfacial resistance between the solid electrolyte and the electrode.

The intermediate layers 150A and 150B preferably include lithium ions and an element capable of forming an intermediate compound. Preferably, the interlayer film may be made of a material including at least one element selected from the group consisting of Au, Ag , Al, Sn, Sb, Si, Ge, C, P, and S. As the carbon source, super P black, amorphous carbon, and graphene may be used.

In the present invention, the interlayer films 150A and 150B preferably have a thickness of 1 μm or less. An interlayer thickness exceeding 1 μm is not preferable in terms of low lithium ion conductivity compared to conventional separators.

In addition, the interlayer film may be applied in the form of a slurry on the solid electrolyte or may be provided by various methods such as a deposition method such as stuttering.

For example, an interlayer of super P black, amorphous carbon, graphene, or the like on the surface of the solid electrolyte may be provided by applying a slurry. At this time, N-methyl-2-pyrrolidone (NMP) may be used as a solvent for the preparation of the slurry, and the slurry may be prepared by adding about 5 wt% of carbon powder and stirring for 24 hours. After coating the prepared slurry on the surface of the solid electrolyte membrane (separator) with a brush or the like, drying at room temperature for 3 hours, and vacuum drying at 100° C. for 12 hours, the intermediate membrane can be formed.

On the other hand, in the case of a metal coating such as Au, Ag, Al, Sn, Sb, Si, Ge, it can be prepared by sputtering on the surface of the solid electrolyte membrane.

In the present invention, it is preferable that the interlayers 150A and 150B react with lithium electrochemically during the formation process after the battery is manufactured to form an intermediate phase containing lithium between the solid electrolyte and the electrode. The mesophase formed ensures the passage of lithium ions and electrons. In the present invention, the intermediate phase may be an alloy of lithium and an element constituting an intermediate film or a compound thereof. Therefore, in the present invention, the interlayer film may be formed by a compound other than a compound formed by the reaction between Au, Ag, Al, Sn, Sb, Si, Ge, C, P, or graphene, which is an interlayer film forming element, and Li of the element. Substantially free of substances.

In the present invention, the interlayers 150A and 150B may minimize reaction resistance at the interface by inducing the formation of an intermediate phase. This can eliminate the need to add an artificial external compressive stress condition when manufacturing a conventional all-solid-state battery, and can minimize battery quality dispersion due to interfacial resistance dispersion occurring during battery manufacturing. In addition, it is possible to minimize the high resistance increase rate at the interface between the separator and the electrode due to the repeated charge/discharge cycle of the all-solid-state battery even under an environment where no compressive stress is applied.

Meanwhile, in the above-described embodiment, an example has been described in which the interlayer film is formed between both the positive electrode and the negative electrode and the solid electrolyte separator, but in the present invention, the intermediate film may be formed on one side of both interfaces of the solid electrolyte separator. Preferably, the interlayer film may be formed at the interface with the lithium metal negative electrode or the positive electrode.

Hereinafter, preferred embodiments of the present invention will be described.

<Experimental Example 1>

LPSI (Li ₇ P ₂ S ₈ I) or LPSCl (LI ₆ PS ₅ Cl) was used as the solid electrolyte separator. 0.2 g of LPSI (Li ₇ P ₂ S ₈ I) or LPSCl (LI ₆ PS ₅ Cl) solid electrolyte was placed in a mold having a diameter of 16 mm and maintained at a pressure of 5 ton for 3 minutes to prepare a solid electrolyte pellet.

Then, a stainless steel spacer, Li metal plate, solid electrolyte pellet (solid electrolyte-binder separator), Li metal and stainless steel were laminated in this order in a mold with a diameter of 16 mm, and after applying a pressure of 0.5 ton for 1 minute, 2032 coin cell type of the cell was prepared.

Charge-discharge cycle characteristics were evaluated with the prepared cell. The test conditions were a current of 0.1 A/cm ² , a cut-off of 10 min, and a measurement temperature of 25.

2 (a) and (b) are graphs showing the measurement results of the charging and discharging characteristics of the LPSI electrolyte and the LPSCl electrolyte cell in the present experimental example, respectively.

As can be seen from (a) and (b) of Figure 2, it can be seen that the voltage during the charge/discharge cycle shows a stable state within a certain range.

<Experimental Example 2>

A 2032 coin cell was prepared in the same manner as in Experimental Example 1, but the cell was prepared in a non-pressurized state during the lamination process. Charge-discharge characteristics were measured for the prepared cells. Test conditions were the same as those of Experimental Example 1.

3 (a) and (b) are graphs showing the measurement results of the charging and discharging characteristics of the LPSI electrolyte and the LPSCl electrolyte cell in the present experimental example, respectively. The lower part of each figure is a graph showing an enlarged view of each part of the graph corresponding to the initial cycle.

Referring to FIG. 3 , it can be seen that, in the case of cells stacked in a non-pressurized state, the voltage value exhibits a very large fluctuation as the cycle is repeated.

<Example 1>

Using LPSCl (LI ₆ PS ₅ Cl) as a solid electrolyte separator, 0.2 g of LPSCl (LI ₆ PS ₅ Cl) solid electrolyte was placed in a mold with a diameter of 16 mm and maintained at a pressure of 5 ton for 3 minutes to pellet the solid electrolyte. was prepared. Then, a slurry was prepared by mixing amorphous carbon powder with NMP solvent on the surface of the solid electrolyte pellet, coated, and dried to form an interlayer. At this time, coating was performed on one or both surfaces of the solid electrolyte pellets, respectively, in the case of one-sided coating, the coating thickness was 20 μm, and in the case of double-sided coating, the total thickness was 31 μm.

Next, as in Experimental Example 2, a cell was prepared in a non-pressurized state during the lamination process, and the charge/discharge characteristics of the cell were measured.

Figure 4 (a) is a graph showing the charging and discharging characteristics of a cell in which an interlayer film having a thickness of 20 μm is formed on one side of the solid electrolyte pellet, (b) is the charging and discharging characteristic of the cell in which an interlayer film is formed on both sides of the solid electrolyte pellet is a graph showing

Referring to (a) of FIG. 4 , it can be seen that the fluctuation of the voltage value is significantly reduced by the 20 μm-thick interlayer formed on one surface of the solid electrolyte. This is clearly revealed when contrasting with FIG. 3 (b) in which the interlayer does not exist under the same conditions.

On the other hand, when an interlayer film is formed on both sides of the solid electrolyte and the thickness is set to 31 μm, the fluctuation range of the voltage value is rather increased. is showing up It can be seen that, when the intermediate film (carbon layer) coated on the solid electrolyte separator is coated with an excessive thickness, it causes an increase in the interfacial resistance.

<Example 2>

Using LPSI (Li ₇ P ₂ S ₈ I) and LPSCl (LI ₆ PS ₅ Cl) as solid electrolyte separators, respectively, 0.2 g of LPSCl (LI ₆ PS ₅ Cl) solid electrolyte was placed in a mold with a diameter of 16 mm and 5 Ton pressure was maintained for 3 minutes to prepare solid electrolyte pellets. Subsequently, Au was sputtered on both sides of the solid electrolyte pellet to form an interlayer film having a thickness of less than 1 μm. Next, as in Example 1, a cell was prepared in a non-pressurized state during the lamination process, and the charge/discharge characteristics of the cell were measured.

Figure 5 (a) is a graph showing the charging and discharging characteristics of the cell in which the interlayer film is formed on the LPSI pellets, (b) is a graph showing the charging and discharging characteristics of the cell in which the interlayer film is formed on the LPSI pellets

As shown in FIG. 5 , it can be seen that the variation of the voltage value according to the cycle repetition was significantly reduced due to the interposition of the Au interlayer.

<Example 3>

A cell was prepared in the same manner as in Example 2, except that LPSCl as the solid electrolyte separator and an Al film having a thickness of less than 1 μm as the interlayer were formed, and the charge/discharge characteristics of the cell were measured. From FIG. 6 , it can be seen that the variation of the voltage value according to the cycle repetition is significantly reduced due to the interposition of the Al interlayer.

As mentioned above, although the embodiment of the present invention has been described in detail, the scope of the present invention is not limited thereto, and various modifications and improvements that can be made by those skilled in the art using the basic concept of the present invention as defined in the following claims In addition, it will be well understood that it falls within the scope of the present invention.

Claims (5)

In an all-solid Li secondary battery comprising a positive electrode, a solid electrolyte separator containing Li, and a negative electrode,
An interlayer of a material different from that of the solid electrolyte separator is formed on at least one surface of the solid electrolyte separator,
The interlayer is an all-solid-state Li secondary battery, characterized in that it contains at least one element selected from the group consisting of Au, Ag , Al, Sn, Sb, Si and Ge. The all-solid-state Li secondary battery, characterized in that the interlayer includes an intermediate phase that is a reaction product with Li contained in the solid electrolyte. According to claim 1,
The interlayer is an all-solid-state Li secondary battery, characterized in that the thickness is less than 1 ㎛. A method for manufacturing an all-solid Li secondary battery comprising a positive electrode, a solid electrolyte separator containing Li, and a negative electrode, the method comprising:
forming an intermediate film of a material different from that of the solid electrolyte separator on at least one surface of the solid electrolyte separator; and
and laminating the solid electrolyte separator with the interlayer formed thereon with an anode and a cathode,
The intermediate film is a method of manufacturing an all-solid-state Li secondary battery, characterized in that it contains at least one element selected from the group consisting of Au, Ag , Al, Sn, Sb, Si and Ge. 5. The method of claim 4,
The lamination step is a method of manufacturing an all-solid-state secondary battery, characterized in that it is performed in a non-pressurized state.

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