CN116601803A

CN116601803A - Composite for positive electrode active material, positive electrode for secondary battery comprising same, and secondary battery comprising same

Info

Publication number: CN116601803A
Application number: CN202280008168.XA
Authority: CN
Inventors: 金明洙; 金明星; 金泰坤
Original assignee: LG Energy Solution Ltd
Current assignee: LG Energy Solution Ltd
Priority date: 2021-08-17
Filing date: 2022-08-01
Publication date: 2023-08-15

Abstract

The present application provides a positive electrode active material composite, a secondary battery electrode including the same, and a secondary battery including the electrode, the positive electrode active material composite including: a positive electrode active material; and a coating layer formed on the pores and the surface of the positive electrode active material, wherein the coating layer is formed of a coating composition comprising a conductive material powder and a solid electrolyte powder having a particle diameter (D50) of 0.3 μm to 2 μm.

Description

Composite for positive electrode active material, positive electrode for secondary battery comprising same, and secondary battery comprising same

Technical Field

The present application claims priority based on korean patent application No. 10-2021-0108241 filed on day 8 and 17 of 2021 and korean patent application No. 10-2022-0092845 filed on day 7 and 27 of 2022, which are incorporated herein by reference in their entireties.

The present application relates to a composite for a positive electrode active material, a positive electrode for a secondary battery including the same, and a secondary battery including the positive electrode.

Background

Recently there has been increasing interest in energy storage technology. As its application field expands to energy sources of mobile phones, video cameras, notebook computers, and even electric automobiles, research and development work of electrochemical devices is being more and more specifically conducted.

Electrochemical devices are the most notable field in this respect, and among them, development of secondary batteries capable of charge/discharge is a focus of attention. Recently, in order to improve the capacity density and specific energy in developing secondary batteries, research and development of new electrode designs and battery designs are actively being conducted.

Currently, among secondary batteries that have been put into practical use, lithium ion batteries are in the spotlight due to their advantages of higher operating voltage and significantly higher energy density as compared to conventional batteries.

However, since the lithium ion battery using the electrolyte has a structure in which the negative electrode and the positive electrode are separated by the separator, if the separator is damaged by deformation or external impact, a short circuit may occur, which may cause a risk of overheating or explosion. In order to solve the above problems, solid electrolyte materials using ion conductive polymers or inorganic materials and all-solid batteries using these materials are being developed.

The lithium ion secondary battery using the solid electrolyte has advantages in that the safety of the battery is improved, leakage of an electrolyte can be prevented, thereby improving the reliability of the battery, and in that it is easy to manufacture a thin battery. These solid electrolytes can be broadly classified into polymer electrolyte materials and inorganic solid electrolyte materials according to the characteristics of the materials. The use of solid electrolytes is known to be advantageous in terms of battery performance such as safety, high energy density, high output, and long life, and is even advantageous in terms of simplifying the manufacturing process, expanding/compressing the battery, and reducing the cost, and thus has recently attracted increasing attention.

The lithium ion conductivity of the solid electrolyte is still lower than that of the electrolyte, however, in theory, since the ion conductivity in the solid is reported to be higher than that of the liquid, an all-solid lithium ion battery is attracting attention from the viewpoints of charge-discharge rate and high output. When a solid electrolyte is used, the active material and the electrolyte must be in close contact to ensure ionic conductivity. Therefore, a technique of forming close contact between an active material and an electrolyte by applying high voltage at the time of manufacturing an electrode is known.

However, in the case of simply applying high pressure as in the prior art, in many cases, contact between the active material and the electrolyte is not sufficiently achieved due to the high pressure, and since there is a fear that the electrode and/or the solid electrolyte may be damaged due to the high pressure pressurization, it is necessary to develop a more effective method.

Meanwhile, when a solid electrolyte is used, not only the close contact between the active material and the electrolyte but also the close contact between the active material and the conductive material is required.

However, the current method of manufacturing an electrode of an all-solid battery is mainly performed by a method of simply mixing components, and the resistance of the electrode cannot be sufficiently reduced due to the limitations of such a method.

[ Prior Art literature ]

Korean laid-open patent No. 10-2015-0064697

Disclosure of Invention

[ technical problem ]

The present application has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present application is to provide a composite for a positive electrode active material capable of providing excellent ionic conductivity and electronic conductivity by forming a structure in which a positive electrode active material is in close contact with a solid electrolyte and a conductive material, a positive electrode for a secondary battery including the same, and a secondary battery including the positive electrode.

Technical scheme

In order to achieve the above object, the present application provides a composite for a positive electrode active material, comprising:

a positive electrode active material; and

a coating layer formed on the pores and the surface of the positive electrode active material,

wherein the coating layer is formed of a coating composition comprising a conductive material powder and a solid electrolyte powder having a particle diameter (D50) of 0.3 μm to 2 μm.

The present application also provides a positive electrode for a secondary battery comprising the composite for a positive electrode active material.

In addition, the present application provides a secondary battery comprising the above-described positive electrode, negative electrode, and solid electrolyte.

[ advantageous effects ]

The composite for a positive electrode active material of the present application provides excellent ionic conductivity and electron conductivity by forming a coating layer on the surface of the positive electrode active material and the inside of its pores with a solid electrolyte and a conductive material, thereby forming a structure in which the positive electrode active material is in close contact with the solid electrolyte and the conductive material.

In addition, the positive electrode for a secondary battery including the composite for a positive electrode active material provides excellent ion conductivity and electron conductivity.

In addition, the secondary battery including the positive electrode provides improved battery capacity, improved charge-discharge characteristics, and life characteristics due to the improvement in performance of the positive electrode as described above.

Drawings

Fig. 1 is a diagram schematically showing the structure of a composite for a positive electrode active material of the present application.

Detailed Description

The present application will be described in more detail below to aid in understanding the present application.

The terms and words used in the present specification and claims should not be construed as limited to common terms or dictionary terms, but should be construed as meaning and concept consistent with the technical ideas of the present application based on the principle that the inventor can properly define the concept of terms to describe the application in the best possible manner.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

It should be understood that the terms "comprises" or "comprising," when used in this specification, are intended to specify the presence of stated features, integers, steps, components, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

The composite for a positive electrode active material of the present application includes a positive electrode active material and a coating layer formed on pores and surfaces of the positive electrode active material, wherein the coating layer is formed of a coating composition containing a conductive material powder and a solid electrolyte powder having a particle diameter (D50) of 0.3 μm to 2 μm.

The coating may be a dry coating. In the case of the conventional dry coating method, it is impossible to form a dry coating layer of the same quality as the present application, and according to the present application, a high-quality dry coating layer can be easily formed.

In the case of the dry coating process, since it does not use a solvent, a mixing process, a heat treatment process, or a drying process is not required, so that the process can be shortened, and since side reactions and impurities do not occur, an effect of further reducing surface resistance is provided. In addition, in the case of the wet process, since the solid electrolyte and the conductive material are phase-separated when dried, it is difficult to form a coating layer uniformly mixed with the solid electrolyte and the conductive material on the surface of the active material, and thus the resistance also increases. However, in the case of the dry coating process, since it does not have such drawbacks, excellent performance is provided.

The composite for a positive electrode active material of the present application is characterized in that pores and surfaces of the positive electrode active material are coated with a coating composition comprising a conductive material powder and a solid electrolyte powder. By such coating, since a coating layer formed of a conductive material and a solid electrolyte is formed to the surface of the positive electrode active material and the inside of the pores (pore walls, pore bottoms, inside pores, etc.), close contact can be formed between the positive electrode active material and the solid electrolyte and the conductive material, and thus the composite for the positive electrode active material has excellent ionic conductivity and electronic conductivity.

In one embodiment of the present application, the particle diameter (D50) of the solid electrolyte may be 0.2 μm to 2 μm. The particle diameter (D50) of the solid electrolyte may be 0.3 μm or more and 0.5 μm or more and 0.7 μm or more and 0.9 μm or more and 1.0 μm or more and 1.2 μm or more and 1.8 μm or less, 1.6 μm or less, 1.4 μm or less, 1.2 μm or less, 1.0 μm or less, 0.8 μm or less, 0.6 μm or less, or 0.4 μm or less.

As described above, when a small particle diameter solid electrolyte powder is used, the coating layer on the surface of the positive electrode active material can be made more uniform, and in particular, since the inside of the pores contained in the positive electrode active material is coated with the solid electrolyte, the ion conductivity of the composite for the positive electrode active material can be significantly improved. However, if the particle diameter (D50) of the solid electrolyte is less than 0.2 μm, it is not preferable because particles are scattered and difficult to handle during dry mixing. If the particle diameter (D50) of the solid electrolyte exceeds 2 μm, it is difficult to insert the solid electrolyte powder into the pores of the positive electrode active material, and thus it is not preferable.

In one embodiment of the present application, the positive electrode active material may include pores having a diameter (D50) of 0.5 μm to 3 μm. If the positive electrode active material contains pores having a diameter within the above range, it is preferable because the solid electrolyte powder and the conductive material powder can easily penetrate into the pores, and thus the pore walls and the pore bottoms can be smoothly coated.

In one embodiment of the present application, in particular, it is preferable that the particle diameter (D50) of the solid electrolyte may be smaller than the pore diameter (D50) of the positive electrode active material particles. In addition, it may be more preferable that the ratio of the particle diameter (D50) of the solid electrolyte to the pore diameter (D50) of the positive electrode active material particles is 1:4.5 to 2:3, more preferably 1:3 to 1:2. If these conditions are satisfied, particles of the solid electrolyte easily penetrate into pores of the positive electrode active material, and thus pore walls, pore bottoms, and the like can be smoothly coated, so that it is preferable.

In one embodiment of the present application, for the conductive material powder for the positive electrode, a component known in the art may be used without limitation, for example, those having a particle diameter (D50) of 0.02 μm to 2 μm may be used. If a fiber-type powder satisfying the particle size range is used, the particle size (D50) represents the length of the fiber powder.

In one embodiment of the present application, the positive electrode conductive material powder may preferably have a particle diameter that can be inserted into the pores of the positive electrode active material. In this case, the particle diameter (D50) of the positive electrode conductive material powder may be 0.02 μm to 2 μm. The particle diameter (D50) of the conductive material may be 0.05 μm or more, 0.09 μm or more, 0.2 μm or more, 0.5 μm or more, 0.7 μm or more, 1.0 μm or more, or 1.2 μm or more, and 1.8 μm or less, 1.4 μm or less, 1.0 μm or less, 0.6 μm or less, 0.2 μm or less, 0.1 μm or less, 0.08 μm or less, or 0.05 μm or less.

As described above, if a conductive material powder having a small particle diameter is used, the coating layer on the surface of the positive electrode active material can be made more uniform, and in particular, the inside of the pores contained in the positive electrode active material is coated with the conductive material, and thus the electron conductivity of the composite for the positive electrode active material can be significantly improved. However, if the particle diameter (D50) of the conductive material powder is less than 0.02 μm, it is not preferable because the particles are scattered during dry mixing, making it difficult to handle. If the particle diameter (D50) of the conductive material powder exceeds 2 μm, it is not preferable because it is difficult to insert the conductive material powder into the pores of the positive electrode active material.

In one embodiment of the present application, it is preferable that the particle diameter (D50) of the conductive material powder is smaller than the pore diameter (D50) of the positive electrode active material particles. In addition, the ratio of the particle diameter (D50) of the conductive material powder to the pore diameter (D50) of the positive electrode active material particles is more preferably 1:20 to 1:3, and still more preferably 1:15 to 1:5. If these conditions are satisfied, the conductive material powder easily penetrates into the pores of the positive electrode active material, and thus the pore wall, the pore bottom, and the like can be smoothly coated, so that it is preferable.

In one embodiment of the present application, the ratio of the particle diameter (D50) of the conductive material powder to the particle diameter of the solid electrolyte may be 1:200 to 1:10, more preferably 1:160 to 1:50.

In the present application, the particle diameter of the positive electrode active material, the particle diameter of the solid electrolyte, and the particle diameter of the conductive material can be measured using a Mastersizer 3000 (manufactured by Malvern corporation), and the Mastersizer 3000 is a device for performing wet particle diameter measurement by a laser scattering method.

In addition, the pore diameter of the positive electrode active material may be measured using an FE-SEM device, and in particular, may be measured using a JSM-7200F device (manufactured by JEOL corporation).

In one embodiment of the present application, the weight ratio of the conductive material and the solid electrolyte included in the coating composition may be 0.2:9.8 to 6:4, preferably 0.7:9.3 to 3:7, more preferably 0.8:9.2 to 1.5:8.5.

If the weight ratio of the conductive material is less than the above range, the electron conductivity of the composite for the positive electrode active material may be lowered. If the weight ratio of the conductive material exceeds the above range, the content of the other components is reduced although the electron conductivity is improved, so that it is not preferable.

In addition, if the weight ratio of the solid electrolyte is less than the above range, the ionic conductivity of the composite for the positive electrode active material may be lowered. If the weight ratio of the solid electrolyte exceeds the above range, the content of other components decreases although the ionic conductivity increases, so that it is not preferable.

In one embodiment of the present application, the total weight of the conductive material and the solid electrolyte used in the coating of the positive electrode active material may be 2 to 50 parts by weight, preferably 3 to 20 parts by weight, more preferably 5 to 15 parts by weight, with respect to 100 parts by weight of the composite for the positive electrode active material.

If the total weight of the conductive material and the solid electrolyte is less than the above range, the electron conductivity and the ion conductivity of the composite for the positive electrode active material may be lowered. If the total weight exceeds the above range, although the electron conductivity and the ion conductivity may be improved, the content of the positive electrode active material may be reduced, and thus the capacity of the electrode may be reduced, so that it is not preferable.

In one embodiment of the present application, the particle diameter (D50) of the positive electrode active material may be 3 μm to 30 μm. If the particle diameter (D50) is smaller than the above range, it is not preferable because the coating layer of the solid electrolyte and the conductive material may be formed unevenly and the solid electrolyte and/or the conductive material is difficult to penetrate into the pores of the active material. If the particle diameter (D50) exceeds the above range, the coating properties are improved, but the active material is broken by friction during the second high shear mixing, possibly causing side reactions, so that it is not preferable.

In one embodiment of the present application, the positive electrode active material may be at least one selected from the group consisting of NCM, LFP, LMO, LCO and the like, and specifically may be any one active material particle selected from the group consisting of: liCoO ₂ 、LiNiO ₂ 、LiMn ₂ O ₄ 、LiCoPO ₄ 、LiFePO ₄ And LiNi _1-x-y-z Co _x M1 _y M2 _z O ₂ (wherein M1 and M2 are each independently any one selected from the group consisting of Al, ni, co, fe, mn, V, cr, ti, W, ta, mg and Mo, and x, y and z are each independently an atomic fraction of an element constituting an oxide, and 0.ltoreq.x)<0.5、0≤y<0.5、0≤z<0.5、0<x+y+z.ltoreq.1). However, the positive electrode active material is not limited thereto.

The content of the positive electrode active material may be 50 to 98 wt% based on 100 parts by weight of the composite for the positive electrode active material.

In one embodiment of the present application, the solid electrolyte powder may be a solid electrolyte powder as exemplified below. The solid electrolyte includes a solid electrolyte material having ion conductivity, and may include a solidPolymer electrolytes, inorganic solid electrolytes, or a mixture of both. The solid electrolyte preferably exhibits 10 ^-7 Ion conductivity of s/cm or more.

In one embodiment of the present application, the solid polymer electrolyte may be a solid polymer electrolyte formed by adding a polymer resin to a solvated lithium salt, or a polymer gel electrolyte formed by accommodating an organic electrolyte containing an organic solvent and a lithium salt in a polymer resin.

The solid polymer electrolyte may include, for example, one selected from the group consisting of: the polyether polymer, the polycarbonate polymer, the acrylic polymer, the polysiloxane polymer, the phosphazene polymer, the polyethylene derivative, the alkylene oxide derivative, the phosphate polymer, the poly-stirring lysine, the polyester sulfide, the polyvinyl alcohol, the polyvinylidene fluoride, and the polymer containing an ion dissociating group, or a mixture of two or more thereof, but is not limited thereto.

In one embodiment of the present application, the solid polymer electrolyte may include one selected from the group consisting of: branched copolymers obtained by copolymerizing amorphous polymers such as PMMA, polycarbonate, polysiloxanes (pdms) and/or phosphazenes as comonomers in PEO (polyethylene oxide) main chains as polymer resins, comb-shaped polymer resins and crosslinked polymer resins, or mixtures of two or more thereof.

Further, in one embodiment of the present application, the polymer gel electrolyte may include an organic electrolytic solution including a lithium salt and a polymer resin, and the content of the organic electrolytic solution may be 60 to 400 parts by weight with respect to the weight of the polymer resin. The polymer resin applied to the gel electrolyte is not limited to a specific component, but may be, for example, one selected from the group consisting of: polyvinyl chloride (PVC), poly (methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), and poly (vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), or a mixture of two or more thereof, but is not limited thereto.

In the electrolyte of the applicationWherein the above lithium salt is an ionizable lithium salt and may be represented by Li ⁺ X ^- . The anion (X) of the lithium salt is not particularly limited, and may be F ^- 、Cl ^- 、Br ^- 、I ^- 、NO ₃ ^- 、N(CN) ₂ ^- 、BF ₄ ^- 、ClO ₄ ^- 、PF ₆ ^- 、(CF ₃ ) ₂ PF ₄ ^- 、(CF ₃ ) ₃ PF ₃ ^- 、(CF ₃ ) ₄ PF ₂ ^- 、(CF ₃ ) ₅ PF ^- 、(CF ₃ ) ₆ P ^- 、CF ₃ SO ₃ ^- 、CF ₃ CF ₂ SO ₃ ^- 、(CF ₃ SO ₂ ) ₂ N ^- 、(FSO ₂ ) ₂ N ^- 、CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- 、(CF ₃ SO ₂ ) ₂ CH ^- 、(SF ₅ ) ₃ C ^- 、(CF ₃ SO ₂ ) ₃ C ^- 、CF ₃ (CF ₂ ) ₇ SO ₃ ^- 、CF ₃ CO ₂ ^- 、CH ₃ CO ₂ ^- 、SCN ^- 、(CF ₃ CF ₂ SO ₂ ) ₂ N ^- Etc.

Meanwhile, in the embodiment of the present application, the polymer-based solid electrolyte may further include an additional polymer gel electrolyte. The polymer gel electrolyte has excellent ionic conductivity (or 10 ^-4 s/m or more) and has adhesion, thereby providing not only a function as an electrolyte but also a function of an electrode binder resin that provides a binding force between electrode active materials and a binding force between an electrode layer and a current collector.

Meanwhile, in the present application, the inorganic solid electrolyte may include a sulfide-based solid electrolyte and/or an oxide-based solid electrolyte.

In a specific embodiment of the present application, the sulfide-based solid electrolyte isThe component containing sulfur atoms in the electrolyte component is not particularly limited to a specific component, and may be at least one of a crystalline solid electrolyte, an amorphous solid electrolyte (vitreous solid electrolyte), and a glass ceramic solid electrolyte. Specific examples of the sulfide-based solid electrolyte may include, but are not limited to, thio-LISICON-based compounds, such as LPS-type sulfides (e.g., li) containing sulfur and phosphorus ₂ S-P ₂ S ₅ )、Li _4-x Ge _1- _x P _x S ₄ (wherein x is 0.1 to 2, specifically, x is 3/4, 2/3), li _10±1 MP ₂ X ₁₂ (M＝Ge,Si,Sn,Al,X＝S,Se)、Li _3.833 Sn _0.833 As _0.166 S ₄ 、Li ₄ SnS ₄ 、Li _3.25 Ge _0.25 P _0.75 S ₄ 、Li ₂ SP ₂ S ₅ 、B ₂ S ₃ -Li ₂ S、xLi ₂ S-(100-x)P ₂ S ₅ (wherein x is 70 to 80), li ₂ S-SiS ₂ -Li ₃ N、Li ₂ S-P ₂ S ₅ -LiI、Li ₂ S-SiS ₂ -LiI、Li ₂ SB ₂ S ₃ ^- LiI、Li ₁₀ SnP ₂ S ₁₂ And Li (lithium) _3.25 Ge _0.25 P _0.75 S ₄ 。

In a specific embodiment of the present application, the oxide-based solid electrolyte may be LLTO-based compound ((La, li) TiO) ₃ )、Li ₆ La ₂ CaTa ₆ O ₁₂ 、Li ₆ La ₂ ANb ₂ O ₁₂ (wherein A is Ca and/or Sr), li ₂ Nd ₃ TeSbO ₁₂ 、Li ₃ BO _2.5 N _0.5 、Li ₉ SiAlO ₈ LAGP compounds (Li) _1+x Al _x Ge _2-x (PO ₄ ) ₃ Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1), LATP compound (such as Li) ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ )(Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ Wherein 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1)), li _1+x Ti _2-x Al _x Si _y (PO ₄ ) _3-y (wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1), liAl _x Zr _2-x (PO ₄ ) ₃ (wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1), liTi _x Zr _2-x (PO ₄ ) ₃ (wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1), LPS compounds (such as Li) ₂ S-P ₂ S ₅ )、Li _3.833 Sn _0.833 As _0.166 S ₄ 、Li ₄ SnS ₄ 、Li _3.25 Ge _0.25 P _0.75 S ₄ 、B ₂ S ₃ -Li ₂ S、xLi ₂ S-(100-x)P ₂ S ₅ (wherein x is 70 to 80), li ₂ S-SiS ₂ -Li ₃ N、Li ₂ S-P ₂ S ₅ -LiI、Li ₂ S-SiS ₂ -LiI、Li ₂ S-B ₂ S ₃ -LiI、Li ₃ N, LISICON, LIPON Compound (Li) ₃₊ _y PO _4-x N _x Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1), thio-LISICON compounds (such as Li) _3.25 Ge _0.25 P _0.75 S ₄ ) Perovskite compound ((La, li) TiO) ₃ ) Nasicon-like compounds (e.g. LiTi ₂ (PO ₄ ) ₃ ) LLZO-based compounds containing lithium, lanthanum, zirconium, oxygen as components, and may include one or more thereof. However, the present application is not particularly limited thereto.

In one embodiment of the present application, a sulfide-based solid electrolyte may be preferably used as the solid electrolyte.

In one embodiment of the present application, the conductive material powder is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, and for example, may include one selected from the group consisting of: graphite, such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; a graphene; a carbon nanotube; carbon fluoride, metal powders (e.g., aluminum powder and nickel powder); conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; such as a polyphenylene derivative, or a mixture of two or more thereof.

Hereinafter, a compound for a positive electrode active material, a positive electrode for a secondary battery including the same, and the manufacture of a secondary battery including the positive electrode will be described.

< preparation of composite for cathode active Material >

It can be prepared by the following steps: dry-mixing a positive electrode active material, a conductive material powder, and a solid electrolyte powder to prepare a mixture (primary mixing); the mixture was subjected to high shear force (secondary mixing).

The primary mixing may be performed by mixing for 30 seconds to 5 minutes without solvent at 4000 to 6000rpm using a mixer (e.g., lab Blender, waring company).

The secondary mixing may be performed by applying a shearing force of 100N to 250N to the first mixture to perform high shear mixing (for example, NOB-130,Hosokawa micron company) at 2000rpm to 4000rpm for 5 minutes to 20 minutes.

A composite for a positive electrode active material formed by coating the conductive material powder and the solid electrolyte powder on the surface and pores of the positive electrode active material by the above-described method can be prepared.

The composite for a positive electrode active material prepared as described above may have a particle diameter (D50) of 3.5 μm to 40 μm, and the composite for a positive electrode active material may be used as it is, or may be used by selecting particles having a particle diameter within a certain range from them. For example, a particle size (D50) of 5 μm to 20 μm can be selected.

As the mixer and the high shear mixing device for primary mixing and secondary mixing, those known in the art can be used without limitation.

< production of Positive electrode for Secondary Battery >

The positive electrode for a secondary battery of the present application can be manufactured by pressing the composite for a positive electrode active material prepared as described above to prepare a free-standing film, and laminating the free-standing film onto a current collector. Free standing films can be manufactured by pressing using a two roll mill MR-3 (Inoue corporation).

As the current collector, a known current collector used in a secondary battery may be used without limitation, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper; stainless steel surface-treated with carbon, nickel, titanium or silver; a non-conductive polymer surface-treated with a conductive material; a non-conductive polymer surface-treated with a metal; conductive polymers, and the like.

Specifically, the manufacturing of the positive electrode for the secondary battery may include the steps of: pressing the composite for a positive electrode active material prepared as above to manufacture a free-standing film; the prepared free-standing film was laminated on a current collector. The above steps may be performed by methods known in the art.

In addition, the free-standing film may be prepared by additionally mixing an adhesive during the preparation of the free-standing film.

In addition, a conductive material and a solid electrolyte may be further added at the time of manufacturing the free-standing film.

In addition, the positive electrode for a secondary battery of the present application may be manufactured by preparing a wet coating composition from the corresponding components and coating it on a current collector, in addition to the free-standing film manufactured by the dry method as described above.

Wherein the free-standing film may include 80 to 90 wt% of the positive electrode active material, 0 to 10 wt% of the conductive material, and 0 to 15 wt% of the solid electrolyte, with respect to the total weight. Further, when the binder is contained, the content of the binder may exceed 0 to 5% by weight.

Wherein the conductive material and the solid electrolyte may be the same as described above.

The binder is not particularly limited as long as it is a component contributing to the binding of the composite for a positive electrode active material and the conductive material and the current collector, and for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), H-NBR, polyvinylidene fluoride-polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like can be used.

< production of Secondary Battery >

In the present application, the secondary battery refers to any type of secondary battery including the composite for a positive electrode active material. An example of the secondary battery may be a lithium secondary battery, and in particular, since the composite for a positive electrode active material may be preferably applied to an all-solid-state battery, the secondary battery includes an all-solid-state battery.

The following is an explanation of an example of the production of an all-solid-state battery.

An all-solid battery comprises a positive electrode, a negative electrode, and a solid electrolyte membrane disposed between the positive and negative electrodes, wherein the positive electrode is an electrode of the present application and has the above-described construction features.

As the solid electrolyte membrane, any one known in the art may be used without limitation, and for example, it may be prepared from the above-described solid electrolyte. In addition, the solid electrolyte membrane may be in a form that also includes a known separator.

The anode may include, for example, a current collector and an anode active material layer formed on at least one side of the current collector. As the anode, any anode known in the art may be used.

Specifically, the anode active material layer may contain an anode active material, a solid electrolyte, and a conductive material. In addition, the anode active material layer may further include a binder material.

The anode active material may be any one selected from the group consisting of: carbonaceous materials such as natural graphite or artificial graphite (mesophase carbon microbeads (MCMB), pyrolytic carbon, mesophase pitch-based carbon fibers, liquid crystal phase pitch (mesophase pitch), petroleum and coal-based cokes (petroleum or coal tar pitch-derived cokes), and the like); lithium-containing titanium composite oxide (LTO), si, sn, li, zn, mg, cd, ce, ni, or Fe metal (Me); an alloy consisting of the above metals (Me); oxides (MeOx, e.g., SIO) of the above metals (Me); and a complex of the metal (Me) and carbon, or a mixture of two or more thereof.

The conductive material, solid electrolyte, and binder may be the same as those described above.

As for the above-described parts, regarding the construction and manufacturing method of the secondary battery of the present application, the configuration and manufacturing method known in the art may be used without limitation.

Hereinafter, examples will be given to describe the present application in detail. However, the embodiments of the present application may be modified in various other forms, and the scope of the present application should not be construed as being limited to the examples described below. The embodiments of the present application are provided to more fully explain the present application to those skilled in the art.

Example 1-1: preparation of composite for positive electrode active Material

80g of NCM powder, which is positive electrode active material particles having pores with a pore diameter (D50) of 0.5 μm, 9.7g of Li with a particle diameter (D50) of 0.4 μm were mixed using Lab Blender (Waring Co.) as a mixer ₂ S-P ₂ S ₅ The powder and 0.3g of ECP600JD powder (Lion) having a particle diameter (D50) of 0.034 μm were mixed at 5000rpm for 1 minute without solvent (primary mixing). Then, a shearing force of 150N was applied to the mixture, whereby high-shear mixing (using NOB-130,Hosokawa micron Co.) was performed at 3000rpm for 10 minutes (secondary mixing) to prepare a composite for a positive electrode active material having a particle diameter (D50) of 6.2 μm, in which a coating layer was formed on the pores and the surface of the positive electrode active material.

Examples 2-1 to 6-1 and comparative examples 1-1 to 9-1: preparation of composite for positive electrode active material

A composite for a positive electrode active material was prepared in the same manner as in example 1 using each of the components listed in table 1 below.

Comparative example 10-1: preparation of wet composite for positive electrode active material

80g of NCM powder (which is positive electrode active material particles having pores with a pore diameter (D50) of 0.5 μm), 9g of Li with a particle diameter (D50) of 0.4 μm were mixed using a planetary mixer HIVIS 2P-03 (manufactured by Primix Co., ltd.) ₂ S-P ₂ S ₅ The powder, 1g of ECP600JD powder (Lion Co.) having a particle size (D50) of 0.034 μm, and 200ml of ethanol were mixed at 500rpm for 20 minutes. Then, a rotary evaporator R-300 (manufactured by BUCHI Co., ltd.) was usedAnd creating) drying the solvent to prepare a composite for the positive electrode active material.

TABLE 1

Examples 1-2 to 6-2 and comparative examples 1-2 to 10-2: manufacturing of positive electrode

90% by weight of the positive electrode active material composites prepared in examples 1-1 to 6-1 and comparative examples 1-1 to 10-1, 5% by weight of Li, were mixed using Lab Blender (Waring Co.) as a mixer ₂ S-P ₂ S ₅ 2% by weight of carbon black powder and 3% by weight of PTFE as a binder were mixed at 5000rpm without solvent for 1 minute (primary mixing). Then, by applying a shearing force of 100N to the mixture, high-shear mixing (using PBV-0.1L, irie Shokai Co.) (secondary mixing) was performed to prepare a dough (dough). The dough was then used to prepare free standing films by a two roll mill MR-3 (Inoue Corp.). Thereafter, a free-standing film was placed on one side of an aluminum current collector having a thickness of 15 μm and pressed to prepare the positive electrodes of examples 1-2 to 6-2 and comparative examples 1-2 to 10-2, respectively.

Examples 1-3 to 6-3 and comparative examples 1-3 to 10-3: fabrication of all-solid-state battery

Using lithium metal as a counter electrode and the respective positive electrodes fabricated in examples 1-2 to 6-2 and comparative examples 1-2 to 9-2, a solid electrolyte membrane (50 μm, li ₂ S-P ₂ S ₅ ) Arranged between electrodes to prepare fixture cells of examples 1-3 to 6-3 and comparative examples 1-3 to 10-3, each having a capacity of 5mAh/cm ² 。

Experimental example 1: evaluation of initial discharge efficiency and Capacity Retention Rate of all solid State Battery

After an operating pressure of 3MPa was applied to each of the solid-state batteries prepared in examples 1-3 to 6-3 and comparative examples 1-3 to 10-3 and charge and discharge at 0.05C/0.05C 2 times at room temperature, the first discharge capacity was measured as an initial discharge capacity. Thereafter, the high-rate discharge capacity was measured by charging and discharging at 0.1C/0.1C and charging and discharging at 0.1C/0.5C. The test results are shown in Table 2.

Table 2:

as can be seen from the results of table 2 above, if the particle diameter (D50) of the solid electrolyte powder used in the preparation of the composite for the positive electrode active material is outside the range of 0.2 μm to 2 μm (composite of comparative examples 1-1 and 2-1), the initial discharge capacity and the high-rate discharge capacity of the all-solid-state batteries (comparative examples 1-3 and 2-3) using the same are significantly reduced. On the other hand, it can be seen that if the particle diameter (D50) of the solid electrolyte powder used in the preparation of the composite for a positive electrode active material satisfies the above-described range (the composites of examples 1-1 to 6-1), the initial discharge capacity and the high-rate discharge capacity of the all-solid-state battery (examples 1-3 to 6-3) using the same are significantly improved.

Meanwhile, it can be seen that when the composite for the positive electrode active material is prepared, if the weight ratio of the conductive material to the solid electrolyte used in coating the active material satisfies the range of 0.2:9.8 to 6:4 (the compositions of examples 1-1 to 6-1), the initial discharge capacity and the high-rate discharge capacity of the all-solid-state battery (examples 1-3 to 6-3) using the same are significantly improved. On the other hand, it can be seen that if the weight ratio of the conductive material and the solid electrolyte is outside the above range (composite of comparative examples 3-1 to 6-1), the initial discharge capacity and the high-rate discharge capacity of all solid-state batteries (comparative examples 3-3 to 6-3) using the same are significantly reduced.

In addition, it can be seen that if the total weight of the conductive material for coating the active material and the solid electrolyte satisfies the range of 2 to 50 parts by weight (the composites of examples 1-1 to 6-1) with respect to 100 parts by weight of the composite for the positive electrode active material, the initial discharge capacity and the high-rate discharge capacity of the all-solid-state battery (examples 1-3 to 6-3) using the same are significantly improved. On the other hand, it can be seen that if the total weight of the conductive material for coating the active material and the solid electrolyte is outside the above range (composite of comparative examples 7-1 to 8-1), both the initial discharge capacity and the high-rate discharge capacity of the all-solid-state battery (comparative examples 7-3 to 8-3) using the same are significantly reduced.

In addition, it can be seen that in the case of manufacturing an all-solid-state battery (comparative example 10-3) using the composite for a positive electrode active material (comparative example 10-1) manufactured by the wet coating method, the initial discharge capacity and the high-rate discharge capacity were significantly reduced as compared to the positive electrode active material manufactured by the dry coating. This result is considered to be because the solid electrolyte is phase-separated from the conductive material during wet coating, and thus a coating layer in which the solid electrolyte and the conductive material are uniformly mixed is not formed on the surface of the active material.

Claims

1. A composite for a positive electrode active material, comprising:

a positive electrode active material; and

a coating layer formed on the pores and the surface of the positive electrode active material;

wherein the coating layer is formed of a coating composition comprising a conductive material powder and a solid electrolyte powder having a particle diameter D50 of 0.3 μm to 2 μm.

2. The composite for a positive electrode active material according to claim 1, wherein the coating layer is a dry coating layer.

3. The composite for a positive electrode active material according to claim 1, wherein the positive electrode active material comprises pores having a diameter D50 of 0.5 μm to 3 μm.

4. The composite for a positive electrode active material according to claim 1, wherein the conductive material powder for the positive electrode has a particle diameter D50 of 0.02 μm to 2 μm.

5. The composite for a positive electrode active material according to claim 1, wherein a weight ratio of the conductive material to the solid electrolyte contained in the coating composition is 0.2:9.8 to 6:4.

6. The composite for a positive electrode active material according to claim 1, wherein the total weight of the conductive material for coating the positive electrode active material and the solid electrolyte is 2 to 50 parts by weight with respect to 100 parts by weight of the composite for a positive electrode active material.

7. The composite for a positive electrode active material according to claim 1, wherein the positive electrode active material is specifically at least one selected from the group consisting of: liCoO ₂ 、LiNiO ₂ 、LiMn ₂ O ₄ 、LiCoPO ₄ 、LiFePO ₄ And LiNi _1-x-y- _z Co _x M1 _y M2 _z O ₂ Wherein M1 and M2 are each independently any one selected from the group consisting of Al, ni, co, fe, mn, V, cr, ti, W, ta, mg and Mo, and x, y and z are each independently an atomic fraction of an element constituting the oxide, and 0.ltoreq.x<0.5、0≤y<0.5、0≤z<0.5、0<x+y+z≤1。

8. The composite for a positive electrode active material according to claim 1, wherein the solid electrolyte powder is a sulfide-based solid electrolyte powder.

9. A positive electrode for a secondary battery comprising the composite for a positive electrode active material according to any one of claims 1 to 8.

10. The positive electrode for a secondary battery according to claim 9, wherein the positive electrode further comprises a conductive material and a solid electrolyte.

11. The positive electrode for a secondary battery according to claim 10, wherein the positive electrode further comprises a binder.

12. A secondary battery comprising the positive electrode, the negative electrode, and the solid electrolyte of claim 9.