KR102707545B1 - Method for manufacturing positive electrode active material for solid secondary battery - Google Patents

Abstract

According to one embodiment of the present invention, a method for manufacturing a cathode active material for a solid secondary battery comprises: a sulfide-based solid electrolyte; and a lithium composite oxide comprising lithium, nickel, and oxygen; and a manufacturing method for forming an oxide coating layer comprising Nb on at least a portion of a surface of the lithium composite oxide, the method comprising: a step of manufacturing a hydroxide precursor comprising nickel; a step of simultaneously adding a Nb salt solution and an acid to the hydroxide precursor to form a coating layer comprising Nb; and a step of mixing the hydroxide precursor on which the coating layer has been formed and a lithium compound and firing the mixture at 700 to 850°C to form an oxide coating layer comprising Nb.

Description

Method for manufacturing positive electrode active material for solid secondary battery

The present invention relates to a method for manufacturing a cathode active material for a solid secondary battery.

Lithium-ion batteries have a much higher energy density per unit volume than other battery systems, and are currently widely used in electronic devices. They are expanding their application range beyond small batteries to include automobiles and energy storage devices.

However, since lithium-ion batteries, which are commonly known, basically use liquid electrolytes, safety issues related to explosion or ignition continue to arise.

As a substitute for these liquid electrolytes, solid secondary batteries using solid electrolytes, which are broadly classified into three types: sulfide-based, polymer-based, and oxide-based, have been proposed. In particular, sulfide-based solid electrolytes have high Li ion conductivity among solid electrolytes, and thus have been the subject of extensive research.

In order to improve the performance of these solid secondary batteries, there has been research on the interface between the positive electrode active material and the solid electrolyte. For example, research has been conducted to suppress the interfacial resistance between the positive electrode active material and the solid electrolyte by coating the positive electrode active material with LiNbO3.

The purpose of the present invention is to improve the ion conductivity of a cathode active material layer while suppressing the interfacial resistance with a sulfide-based solid electrolyte, thereby improving high-rate characteristics and life characteristics.

The present invention relates to a process for coating the surface of a lithium composite oxide included together with a sulfide-based solid electrolyte with LiNbO3, and aims to form a coating layer on the surface of a lithium composite oxide without peeling so as to improve stability while suppressing the interfacial resistance with the sulfide-based solid electrolyte.

According to one embodiment of the present invention, a method for manufacturing a cathode active material for a solid secondary battery comprises: a sulfide-based solid electrolyte; and a lithium composite oxide comprising lithium, nickel, and oxygen; and a manufacturing method for forming an oxide coating layer comprising Nb on at least a portion of a surface of the lithium composite oxide, the method comprising: a step of manufacturing a hydroxide precursor comprising nickel; a step of simultaneously adding a Nb salt solution and an acid to the hydroxide precursor to form a coating layer comprising Nb; and a step of mixing the hydroxide precursor on which the coating layer has been formed and a lithium compound and firing the mixture at 700 to 850°C to form an oxide coating layer comprising Nb.

As an example, the lithium composite oxide may be represented by the following chemical formula 1.

[Chemical Formula 1] LiaNibCocM1dM2eOf

In the chemical formula 1, M1 is Mn or Al, M2 is at least one selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, Bi and F, and M2 necessarily includes Nb, and 0.8≤a≤1.2, 0.01≤b≤0.99, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1 and 0.5≤e≤2.5.

As an example, Nb may be included in an amount of 0.5 to 10 mol% relative to the entire lithium composite oxide.

As an embodiment, the oxide coating layer including Nb may include a compound represented by the following chemical formula 2.

[Chemical formula 2]

LiNbmOn

In the above chemical formula 2, 1≤m≤2 and 1≤n≤5.

As an embodiment, the oxide coating layer including Nb may further include a sulfide-based solid electrolyte.

As an embodiment, the sulfide-based solid electrolyte particles may include an oxide coating layer including Nb occupying at least a portion of the surface.

As an example, the sulfide-based solid electrolyte may have an argyrodite-type crystal structure.

A solid secondary battery according to one embodiment of the present invention includes a positive electrode active material layer including a positive electrode active material manufactured by the above method for manufacturing a positive electrode active material for a solid secondary battery; an anode active material layer including an anode active material; and a sulfide-based solid electrolyte layer between the positive electrode active material layer and the anode active material layer.

The present invention can improve the ion conductivity of a cathode active material layer while suppressing the interfacial resistance with a sulfide-based solid electrolyte, thereby improving high-rate characteristics and life characteristics.

The present invention relates to a process for coating the surface of a lithium composite oxide included together with a sulfide-based solid electrolyte with LiNbO3, wherein a coating layer can be formed on the surface of a lithium composite oxide without peeling so as to improve stability while suppressing interfacial resistance with the sulfide-based solid electrolyte.

Figure 1 illustrates the structure of a sulfide-based solid-state battery of the present invention.

The terms “comprising” and “including” as used herein should be understood as open-ended terms implying the possibility of including other embodiments.

As used herein, the terms “preferred” and “preferably” refer to embodiments of the present invention that can provide certain advantages under certain circumstances, and are not intended to exclude other embodiments from the scope of the present invention.

The cathode active material for a solid secondary battery of the present invention includes a sulfide-based solid electrolyte; and a lithium composite oxide containing lithium, nickel, and oxygen.

The above sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn, m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-LipMOq, p, q are positive numbers, M may be selected from, but is not limited to, one of P, Si, Ge, B, Al, Ga In, Li7-xPS6-xClx, 0≤x≤2, Li7-xPS6-xBrx, 0≤x≤2, and Li7-xPS6-xIx, 0≤x≤2.

More preferably, the sulfide-based solid electrolyte may be selected from Li7-xPS6-xClx, 0≤x≤2, Li7-xPS6-xBrx, 0≤x≤2, and Li7-xPS6-xIx, 0≤x≤2. In particular, since chlorine can form another crystal structure by replacing some of the other elements in the LiPS6 composition, thereby lowering the activation energy, a new path can be secured for the movement of ions. As a more preferable example, 1≤x≤2 may be satisfactorily, more preferably 1.3≤x≤1.7 may be satisfactorily, and most preferably x=1.5.

When the lithium composite oxide of the present invention is mixed with a sulfide-based solid electrolyte having an argyrodite-type crystal structure to form a cathode active material, the internal resistance of the solid battery produced can be reduced, and the contact problem between the electrode and the solid electrolyte can be improved because the grain boundary resistance is low.

The above lithium composite oxide may be included in an amount of 10 to 99 wt% of the cathode active material layer including the cathode active material for the solid secondary battery.

An oxide coating layer containing Nb is formed on at least a portion of the surface of the lithium composite oxide.

As an example, the lithium composite oxide may further include nickel, and the amount may be 60 mol% or more, 70 mol% or more, and more preferably 80 mol% or more relative to the total content of transition metals included to improve the capacity of the sulfide-based solid-state battery.

As an example, the lithium composite oxide may further include cobalt, and the content of the cobalt may be 30 mol% or less, 20 mol% or less, or 10 mol% or less relative to the total content of the transition metal. On the other hand, as another example, the lithium composite oxide may not include cobalt.

As an example, the lithium composite oxide may further include manganese and/or aluminum, and the content of the manganese and/or aluminum may be 30 mol% or less, 20 mol% or less, or 10 mol% or less relative to the total content of the transition metal.

As an example, the lithium composite oxide may further include an M2 element in the following chemical formula 1, and the M2 element may be 20 mol% or less, 10 mol% or less, 5 mol% or less, 3 mol% or less, or 2 mol% or less relative to the total transition metal content.

As an example, the lithium composite oxide may be represented by the following chemical formula 1.

[Chemical Formula 1] LiaNibCocM1dM2eOf In the chemical formula 1, M1 is Mn or Al, M2 is at least one selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, Bi and F, and M2 necessarily includes Nb, and 0.8≤a≤1.2, 0.01≤b≤0.99, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1 and 0.5≤e≤2.5.

As a more preferable example, the lithium composite oxide has a layered structure, and the planes forming the layers of the layered structure may have a crystal orientation in a direction perpendicular to the C-axis. In this case, the mobility of ions included in the positive electrode active material may be improved, and the structural stability of the positive electrode active material may be improved.

As an example, Nb may be included in an amount of 0.5 to 10 mol% relative to the entire lithium composite oxide.

As an embodiment, the oxide coating layer including Nb may include a compound represented by the following chemical formula 2.

[Chemical formula 2]

LiNbmOn

In the above chemical formula 2, 1≤m≤2 and 1≤n≤5.

The present invention can further improve the ion conductivity of the cathode active material layer by including an oxide coating layer containing Nb on the surface of a lithium composite oxide, thereby suppressing the interfacial resistance with a sulfide-based solid electrolyte.

As an example, the cathode active material for the solid secondary battery may further include a binder. The binder may be any binder polymer that is commonly used without limitation. For example, various types of binder polymers such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene butadiene rubber (SBR), and carboxyl methyl cellulose (CMC) may be used.

There is no particular limitation on the above conductive material as long as it is an electronically conductive material that does not cause a chemical change in the electrochemical device. For example, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, etc. can be used. Current commercially available conductive materials include acetylene black series (products from Chevron Chemical Company or Gulf Oil Company, etc.), Ketjen Black EC series (product from Armak Company), Vulcan XC-72 (product from Cabot Company), and Super P (product from MMM).

A method for producing a cathode active material for a solid secondary battery according to one embodiment of the present invention performs a step of producing a hydroxide precursor containing nickel. The method for producing the hydroxide precursor containing nickel may be performed by a co-precipitation method, but is not limited thereto.

Next, a step of forming a coating layer including Nb is performed by simultaneously adding a Nb salt solution and an acid to the hydroxide precursor. The present invention was able to form an efficient Nb coating layer through a process of making the hydroxide precursor into a slurry and simultaneously adding a Nb salt solution and an acid.

The above Nb salt solution is not particularly limited as long as it is a solution containing a Nb salt having sufficiently high solubility in water. The Nb concentration in the above Nb salt solution is preferably 5 to 35 g/L.

At this time, it is preferable to maintain the pH of the slurry at 5 to 11.7.

Next, a step of mixing the hydroxide precursor and the lithium compound on which the coating layer is formed and calcining at 700 to 850°C to form an oxide coating layer including Nb is performed.

In one embodiment, the oxide coating layer including Nb may further include a sulfide-based solid electrolyte. At this time, the sulfide-based solid electrolyte is as described above. By further including the sulfide-based solid electrolyte as well as the oxide including Nb in the coating layer present on the surface of the lithium composite oxide in this way, the interfacial resistance between the lithium composite oxide of the present invention and the sulfide-based solid electrolyte is suppressed, and the ion conductivity of the positive electrode active material layer can be further improved.

As an embodiment, the sulfide-based solid electrolyte particle may include an oxide coating layer including Nb occupying at least a portion of the surface. The oxide coating layer including Nb is as described above in the lithium composite oxide. In this way, by including the oxide coating layer including Nb not only on the surface of the lithium composite oxide particle but also on the sulfide-based solid electrolyte particle included in the cathode active material, the interfacial resistance between the lithium composite oxide of the present invention and the sulfide-based solid electrolyte can be suppressed, and the ion conductivity of the cathode active material layer can be further improved.

As an example, the average particle diameter of the secondary particles of the lithium composite oxide may be 2 to 50 μm, or 10 to 30 μm. The average particle diameter may be defined as a particle diameter corresponding to 50% of the volume accumulation amount in a particle diameter distribution curve of the particles. The average particle diameter may be measured using, for example, a laser diffraction method.

The specific surface area of the above lithium composite oxide can be 2.0 to 8.0 m2/g.

The cathode active material included in the above cathode active material layer is as described above.

Except for the above-described technical features of the present invention, there are no particular limitations with respect to the structure, material, and manufacturing method of the positive electrode active material layer, the negative electrode active material layer, and the sulfide-based solid electrolyte layer of the solid secondary battery, as long as they can be applied to the solid secondary battery.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples.

<Example 1>

A spherical Ni0.92Co0.08(OH)2 hydroxide precursor was synthesized by a co-precipitation method. In a 90 L reactor, 25 wt% NaOH and 30 wt% NH4OH were added to a 1.5 M complex transition metal sulfate aqueous solution in which NiSO4·7H2O and CoSO4·7H2O were mixed in a molar ratio of 92:8. The pH in the reactor was maintained at 11.5 and the reactor temperature at this time was maintained at 60 ℃. An inert gas, N2, was introduced into the reactor to prevent the prepared precursor from being oxidized. After the synthetic stirring was completed, washing and dehydration were performed using a filter press (F/P) device, thereby obtaining Ni0.92Co0.08(OH)2 hydroxide precursor.

Next, Nb2O5 powder was dissolved in the above hydroxide precursor in an alkaline solution so that the Nb concentration was 30 g/L to prepare a Nb salt solution, and then a 25 mass% sulfuric acid aqueous solution was added together to the precursor slurry to form a Nb oxide coating layer.

Next, the above-mentioned manufactured hydroxide and LiOH were mixed so that the Li/Me ratio was 1.02, heated to 500°C, maintained at 500°C for 3 hours, then heated to 775°C and calcined for 12 hours to manufacture Li1.02Ni0.9Co0.05Al0.02Nb0.03O2 lithium composite oxide.

<Comparative Example 1>

A lithium composite oxide was manufactured in the same manner as in Example 1, except that the step of forming a coating layer in Example 1 was not performed.

<Manufacturing Example> Manufacturing of a solid secondary battery

anode

The lithium composite oxide according to the above examples and comparative examples was mixed with Li6PS5Cl solid electrolyte, polytetrafluoroethylene (PTFE) as a binder, and carbon nanofibers (CNF) as a conductive material in a weight ratio of 89:8.8:1.2:1.0 and a xylene solvent to form a positive electrode active material composition in the form of a sheet, and then vacuum dried at 40°C for 8 hours to produce a positive electrode active material layer.

The above-mentioned manufactured positive electrode active material layer was laminated on a carbon-coated Al current collector and pressed using a roll press to prepare a positive electrode.

cathode

After preparing SUS foil as a negative current collector, 6 g of carbon black (CB) was placed in a container, 8 g of NMP solution containing 5 wt% of PVDF binder was added thereto, and mixed to prepare a slurry. The prepared slurry was applied to the upper part of a Ni current collector using a bar coater, and dried in the air at 80°C for 10 minutes to form a carbon layer containing carbon black and silver.

Solid electrolyte layer

A slurry was prepared by mixing 99 parts by weight of Li6PS5Cl, 1 part by weight of poly(styrene-co-butyl acrylate) (8:2 molar ratio), which is an acrylic binder, and 495 parts by weight of xylene. The slurry was applied onto a polyethylene terephthalate (PET) film using a bar coater, and dried in an oven to prepare a solid electrolyte layer.

Solid secondary battery

The above-mentioned manufactured positive electrode, solid electrolyte layer, and negative electrode were sequentially laminated and plate pressed at a pressure of 500 MPa for 1 min to manufacture a unit cell.

<Experimental example>

In order to evaluate the life characteristics of the solid secondary batteries manufactured in the above examples and comparative examples, constant current charging was performed until the voltage reached 4.25 V with a current of 1 C, and then constant voltage charging was performed until the current reached 0.05 C. After the charging was completed, the cell was rested for about 10 minutes, and then constant current discharge was performed until the voltage reached 2.5 V with a current of 1 C. This cycle was repeated 100 times to evaluate the life characteristics.

ITEM Example 1 Comparative Example 1 Lifespan (%, 100 times) 91.2 72.3

1. Bipolar active material layer
2 Sulfide-based solid electrolyte layer
3 Negative active material layer

Claims (8)

A method for manufacturing a lithium composite oxide comprising a sulfide-based solid electrolyte; and lithium, nickel and oxygen; and forming an oxide coating layer comprising Nb on at least a portion of the surface of the lithium composite oxide,
A step of preparing a hydroxide precursor containing nickel;
A step of forming a coating layer including Nb by simultaneously adding a Nb salt solution and an acid to the above hydroxide precursor;
A step of mixing the hydroxide precursor and the lithium compound on which the coating layer is formed and firing them at 700 to 850°C to form an oxide coating layer containing Nb; and
A step of mixing and drying an oxide and a sulfide-based solid electrolyte, wherein the oxide coating layer including Nb is formed so that the sulfide-based solid electrolyte includes a coating layer including Nb on at least a portion of the surface, and the coating layer includes a sulfide-based solid electrolyte;
Method for manufacturing a cathode active material for a solid secondary battery.
In paragraph 1,
The above lithium composite oxide is represented by the following chemical formula 1:
Method for manufacturing positive electrode active material for solid secondary battery:
[Chemical Formula 1] LiaNibCocM1dM2eOf In the chemical formula 1, M1 is Mn or Al, M2 is at least one selected from Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, Bi and F, and M2 necessarily includes Nb, and 0.8≤a≤1.2, 0.01≤b≤0.99, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1 and 0.5≤f≤2.5.
In paragraph 1,
Nb is contained in an amount of 0.5 to 10 mol% relative to the total lithium composite oxide.
Method for manufacturing a cathode active material for a solid secondary battery.
In paragraph 1,
The oxide coating layer containing the above Nb comprises a compound represented by the following chemical formula 2:
Method for manufacturing positive electrode active material for solid secondary battery:
[Chemical formula 2]
LiNbmOn
In the above chemical formula 2, 1≤m≤2 and 1≤n≤5.
delete delete In paragraph 1,
The above sulfide-based solid electrolyte has an argyrodite-type crystal structure.
Method for manufacturing a cathode active material for a solid secondary battery.
A cathode active material layer comprising a cathode active material manufactured by the method for manufacturing a cathode active material for a solid secondary battery according to claim 1;
A negative electrode active material layer including a negative electrode active material; and
Including a sulfide-based solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer,
Solid secondary battery.