WO2024210303A1

WO2024210303A1 - Negative electrode active material, preparation method therefor, negative electrode for all-solid-state rechargeable battery, and all-solid-state rechargeable battery

Info

Publication number: WO2024210303A1
Application number: PCT/KR2024/000419
Authority: WO
Inventors: 김주윤; 민명기; 황수민; 박슬찬; 김진우; 유호선
Original assignee: 삼성에스디아이 주식회사
Priority date: 2023-04-06
Filing date: 2024-01-09
Publication date: 2024-10-10
Also published as: KR20240150656A

Abstract

The present invention relates to a negative electrode active material, a negative electrode for an all-solid-state rechargeable battery, comprising same, and an all-solid-state rechargeable battery, the negative electrode active material comprising: negative electrode active material particles comprising a lithium transition metal composite oxide; and a coating layer positioned on the surface of the negative electrode active material particles, wherein the coating layer comprises an organic material and a lithium salt, and the organic material comprises a (meth)acrylate containing an alkylene glycol unit, an ether containing an alkylene glycol unit, or a combination thereof.

Description

Positive electrode active material and its manufacturing method, positive electrode for all-solid-state secondary battery and all-solid-state secondary battery

The present invention relates to a cathode active material and a method for manufacturing the same, a cathode for an all-solid-state secondary battery, and an all-solid-state secondary battery.

Recently, as the explosion risk of batteries using liquid electrolytes has been reported, the development of all-solid-state secondary batteries is being actively conducted. However, solid electrolytes have problems such as lower ion conductivity than liquid electrolytes, resistance occurs at the interface with solid particles such as positive electrode active materials in the battery, and a depletion layer is formed by the bonding of solids, which reduces ion conductivity.

The cathode for an all-solid-state secondary battery is composed of inorganic materials such as cathode active material, solid electrolyte, and conductive material. Here, the movement of lithium ions at the contact point between the solid particles of the cathode active material and the solid electrolyte has a major impact on the battery performance. However, the volume change of the cathode active material that occurs during the charge/discharge process limits the physical bonding between the cathode active material and the solid electrolyte, and to overcome this, research is continuously being conducted to improve the contact between the particles.

Conventional all-solid-state secondary battery cathodes use a method of fixing the cathode active material and solid electrolyte using a fluorine-based binder to maintain the electrode plate. However, there is a problem in that the fluorine-based binder can hinder lithium movement and reduce the performance of the all-solid-state secondary battery.

By improving the interfacial adhesion between a cathode active material and a solid electrolyte and effectively preventing the deterioration of battery performance due to volume change of the cathode active material according to charge and discharge, the capacity characteristics and life characteristics of an all-solid-state secondary battery are improved.

In one embodiment, a cathode active material is provided, which comprises a cathode active material particle including a lithium transition metal composite oxide, and a coating layer positioned on a surface of the cathode active material particle, wherein the coating layer comprises an organic material and a lithium salt, and the organic material comprises a (meth)acrylate containing an alkylene glycol unit, an ether containing an alkylene glycol unit, or a combination thereof.

In another embodiment, a method for producing a cathode active material is provided, comprising: preparing a composite by mixing an organic material and a lithium salt, mixing the composite with cathode active material particles including a lithium transition metal composite oxide, and drying the composite to coat the surface of the cathode active material particles with the composite, wherein the organic material comprises a (meth)acrylate containing an alkylene glycol unit, an ether containing an alkylene glycol unit, or a combination thereof.

In another embodiment, a positive electrode for an all-solid-state secondary battery is provided, comprising the positive electrode active material and a sulfide-based solid electrolyte.

In another embodiment, an all-solid-state secondary battery is provided, comprising the aforementioned positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and negative electrode.

According to one embodiment, a cathode active material is a material having an organic substance and a lithium salt coated on the surface, which improves the interfacial adhesive strength between the cathode active material and the solid electrolyte, thereby facilitating the movement of lithium ions, effectively preventing degradation of battery performance due to volume change of the cathode active material according to charge and discharge, and improving the overall performance of the all-solid-state secondary battery, such as capacity characteristics and life characteristics.

Figures 1 and 2 are cross-sectional views schematically illustrating an all-solid-state secondary battery according to one embodiment.

Figure 3 is a graph showing the discharge capacity according to the number of cycles for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 and 2.

Figure 4 is a graph showing the capacity retention rate according to the number of cycles for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 and 2.

Hereinafter, specific implementation examples will be described in detail so that those with ordinary skill in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

In order to clearly express various layers and regions in the drawings, the thickness is enlarged and shown, and the same drawing symbols are used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is said to be "over" or "on" another part, this includes not only the case where it is "directly over" the other part, but also the case where there is another part in between. Conversely, when a part is said to be "directly over" another part, it means that there is no other part in between.

Also, the term “layer” here includes not only the shape formed on the entire surface when observed in a flat surface, but also the shape formed on a portion of the surface.

The average particle size can also be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope photograph or a scanning electron microscope photograph. Alternatively, the average particle size can be obtained by measuring using a dynamic light scattering method, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. The average particle size can be measured with a microscope image or a particle size analyzer, and can mean the diameter of particles having a cumulative volume of 50% by volume (D50) in the particle size distribution.

Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

양극 활물질Bipolar active material

The above-mentioned positive electrode active material has excellent adhesion to the solid electrolyte since a specific organic substance and a lithium salt are coated on the surface, and even if the volume of the positive electrode active material changes depending on charge and discharge, stable contact between solid particles within the positive electrode is secured, and accordingly, the movement of lithium ions is facilitated for a long cycle, so that the overall performance of the all-solid-state secondary battery can be improved. When the coated positive electrode active material according to one embodiment is applied to the positive electrode, the adhesion between solid particles is higher and the movement of lithium ions is further promoted compared to a case where the same organic substance and lithium salt are simply dispersed in the positive electrode, so that the life stability of the all-solid-state battery can be further improved.

In the above coating layer, the organic material may be an acrylate or ether containing an alkylene glycol unit, and such an organic material has low reactivity with a sulfide-based solid electrolyte, excellent oxidation resistance, and can implement high adhesion. For example, polyethylene glycol (PEG) has high reactivity with a sulfide-based solid electrolyte, making it difficult to apply it to the positive electrode of an all-solid-state battery, and a general acrylic binder that does not contain an alkylene glycol unit has low oxidation resistance, and thus the binder itself may be decomposed in an all-solid-state battery manufactured under high temperature and high pressure conditions, and thus may not be suitable.

The alkylene glycol may be, but is not limited to, ethylene glycol, propylene glycol, or neopentyl glycol, for example, and may be, for example, ethylene glycol. The number of alkylene glycol units in the organic material may be 1 to 200, for example, 1 to 5, or 20 to 200. In addition, the number of (meth)acrylate groups in the (meth)acrylate containing the alkylene glycol unit may be 1 to 4, for example, 1 or 2. The number of ether groups in the ether containing the alkylene glycol unit may be 1 to 4, for example, 1 or 2. The ether groups may be chain-like or cyclic. The organic material may include only an acrylate group, only an ether group, or both an acrylate group and an ether group.

Specific examples of the (meth)acrylate containing the above alkylene glycol unit, the ether containing the alkylene glycol unit, or the combination thereof may include the following compounds. For example, poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) monoacrylate (PEGMA), poly(propylene glycol) diacrylate (PPGDA), poly(propylene glycol) dimethacrylate (PPGDMA), di(ethylene glycol) diacrylate (DEGDA), tri(ethylene glycol) diacrylate (TEGDA), tetra(ethylene glycol) diacrylate (TTEGDA), di(propylene glycol) diacrylate (DPGDA), tri(propylene glycol) diacrylate (TPGDA), ethoxylated trimethylolpropane triacrylate (ETPTA), poly(ethylene glycol) methyl ether methacrylate (PEGDMA), poly(ethylene glycol) dimethyl ether (PEGDME; polyglime), tri(ethylene glycol) dimethyl ether (triglyme), tetra(ethylene glycol) dimethyl It can be ether (TEGDME, tetraglyme), or a combination of these.

The organic material may include, among these, for example, poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) monoacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (PEGDMA), poly(ethylene glycol) dimethyl ether (PEGDME; polyglime), or a combination thereof, and these have low reactivity with a sulfide-based solid electrolyte, high oxidation resistance, and high adhesive strength, making them suitable for application as a coating component of a cathode active material for an all-solid-state secondary battery.

The above organic substances, i.e., (meth)acrylate containing alkylene glycol units and ether containing alkylene glycol units, may each independently have a number average molecular weight of 200 g/mol to 2,000 g/mol. Their number average molecular weights may be, for example, 250 g/mol to 1,500 g/mol, or 300 g/mol to 1,200 g/mol. When applying organic substances having such molecular weights, a thin coating layer can be formed while implementing excellent adhesive strength.

In the above coating layer, the organic matter and lithium salt may form a kind of complex.

In the coating layer, the organic material may be included in an amount of 20 to 90 wt%, and the lithium salt may be included in an amount of 10 to 80 wt%, based on a total of 100 wt% of the organic material and the lithium salt. When mixed in this ratio, the coating layer can improve performance, such as life stability, of the all-solid-state secondary battery by implementing appropriate adhesive strength and facilitating the movement of lithium ions. The weight ratio of the organic material to the lithium salt in the coating layer may be 2:8 to 9:1, and may be, for example, 2:8 to 8:2, 3:7 to 7:3, or 2:8 to 6:4.

The total content of the organic material and the lithium salt may be 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material particles, for example, 0.1 to 8 parts by weight, 0.1 to 6 parts by weight, 0.1 to 5 parts by weight, 0.5 to 4 parts by weight, or 1 to 3 parts by weight.

Additionally, the organic material may be included in an amount of 0.05 wt% to 5 wt% based on 100 wt% of the positive electrode active material, for example, 0.05 wt% to 4 wt%, 0.1 wt% to 3 wt%, or 0.5 wt% to 2 wt%. The lithium salt may be included in an amount of 0.05 wt% to 5 wt% based on 100 wt% of the positive electrode active material, for example, 0.05 wt% to 4 wt%, 0.1 wt% to 3 wt%, or 0.5 wt% to 2 wt%.

The above lithium salt may be applied without limitation on type, and may include, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiPO ₂ F ₂ , LiCl, LiI, LiSCN, LiN(CN) ₂ , lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, or a combination thereof.

For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof, which may facilitate the movement of lithium ions on the surface of the positive electrode active material.

The above coating layer may exist in the form of an island or a continuous film on the surface of the positive electrode active material particle.

Since the coating layer is composed of an organic material and a lithium salt, it can be formed with a very thin thickness, thereby increasing adhesion and facilitating lithium ions without increasing resistance within the battery. The thickness of the coating layer can be 1 nm to 50 nm, and for example, 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 20 nm, 1 nm to 10 nm, or 2 nm to 10 nm.

The cathode active material particles including the above lithium transition metal composite oxide correspond to a kind of core, and commonly used cathode active material particles can be applied without limitation.

The above lithium transition metal composite oxide may be, for example, lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt oxide (NC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium nickel manganese oxide (NM), lithium manganese oxide (LMO), or lithium iron phosphate (LFP).

The above lithium transition metal composite oxide may be, for example, a lithium nickel-based oxide represented by the following chemical formula 1, a lithium cobalt-based oxide represented by the following chemical formula 2, a lithium iron phosphate-based compound represented by the following chemical formula 3, or a cobalt-free lithium nickel-manganese-based oxide represented by the following chemical formula 4.

[Chemical Formula 1]

Li _a1 Ni _x1 M ¹ _y1 M ² _z1 O _2- _b1

In the chemical formula 11, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, M ¹ and M ² are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, X is one or more elements selected from the group consisting of F, P, and S,

[Chemical formula 2]

Li _a2 Co _x2 M ³ _y2 O _2- _b2

In the chemical formula 2, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, M ³ is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, X is at least one element selected from the group consisting of F, P, and S,

[Chemical Formula 3]

Li _a3 Fe _x3 M ⁴ _y3 PO _4- _b3

In the chemical formula 3, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, M ⁴ is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, X is at least one element selected from the group consisting of F, P, and S,

[Chemical Formula 4]

Li _a4 Ni _x4 Mn _y4 M ⁵ _z4 O _2- _b4

In the chemical formula 4, 0.9≤a4≤1.8, 0.8≤x4<1, 0<y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, and 0≤b4≤0.1, and M ⁵ is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is at least one element selected from the group consisting of F, P, and S.

The above lithium transition metal composite oxide may be a lithium nickel-based oxide represented by the above chemical formula 1, and may be, for example, a high nickel-based oxide. That is, the nickel content with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide may be 80 mol% or more, or 90 mol% or more, or 91 mol% or more, or 94 mol% or more. In the above chemical formula 1, 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2, or 0.9≤x1≤1, 0≤y1≤0.1, and 0≤z1≤0.1, or 0.91≤x1≤1, 0≤y1≤0.09, and 0≤z1≤0.09, or 0.94≤x1≤1, 0≤y1≤0.06, and 0≤z1≤0.06. For example, 0.8≤x1<1, 0<y1≤0.2, and 0≤z1≤0.2 may be satisfied, or 0.9≤x1<1, 0<y1≤0.1, and 0≤z1≤0.1. High-nickel oxides can implement high capacity, and are therefore suitable for application to high-capacity, high-density all-solid-state secondary batteries that have recently been in demand. However, since a cathode active material including a high-nickel oxide has a large volume change of about 8% depending on charge and discharge, it is difficult to maintain long-term contact with a solid electrolyte. However, by introducing a coating layer according to one embodiment, it is possible to implement long-term adhesion between solid particles while facilitating the movement of lithium ions.

The average particle diameter (D50) of the positive active material particles may be 1 ㎛ to 25 ㎛, for example, 2 ㎛ to 20 ㎛, or 3 ㎛ to 18 ㎛. For example, the positive active material particles may include small particles having an average particle diameter (D50) of 1 ㎛ to 9 ㎛ and large particles having an average particle diameter (D50) of 10 ㎛ to 20 ㎛. In this case, the small particles may be included in an amount of 5 wt% to 40 wt% and the large particles may be included in an amount of 60 wt% to 95 wt% with respect to a total of 100 wt% of the small particles and the large particles, for example, the small particles may be included in an amount of 10 wt% to 30 wt% and the large particles may be included in an amount of 70 wt% to 90 wt%. When the positive active material particles are formed by mixing the small particles and the large particles, a high energy density battery can be implemented.

Here, the average particle size may be obtained by randomly measuring the size (diameter or length of the major axis) of about 20 particles in an electron microscope photograph such as a scanning electron microscope to obtain a particle size distribution, and taking the diameter (D50) of the particles having a cumulative volume of 50% by volume in the particle size distribution as the average particle size.

The above-mentioned positive electrode active material particles may be in the form of secondary particles formed by agglomeration of multiple primary particles, in the form of single particles, or in the form of a mixture of these.

For example, both elementary particles and macromolecules can be secondary particles in the form of aggregated multiple primary particles, and these secondary particles can be said to be a type of polycrystal form. Alternatively, the elementary particles can be single particle forms, and the macromolecules can be secondary particles in the form of aggregated multiple primary particles. Here, a single particle means that it exists alone without a grain boundary within the particle and is composed of a single particle, and morphologically, it can mean a single particle, a monolithic structure, a single-body structure, or a non-aggregated particle in which the particles exist as an independent phase without being mutually aggregated, and can be, for example, a single crystal.

Meanwhile, the positive electrode active material may further include a buffer layer between the positive electrode active material particles and the coating layer. The buffer layer may lower the interfacial resistance between the positive electrode active material particles or between the positive electrode active material and the solid electrolyte particles, and may improve the initial charge/discharge efficiency and life characteristics of the battery.

The above buffer layer may include a lithium compound and a metal oxide. The lithium compound means a compound containing lithium, and the metal oxide means an oxide containing a metal other than lithium. Here, the metal is a concept including general metals, transition metals, and metalloids. In the metal oxide, the metal may be at least one element selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr, for example. The lithium compound may be, for example, a carbonate, a hydroxide, an oxide, etc. containing lithium, and may be, for example, Li ₂ CO ₃ , LiOH, or a combination thereof.

The above buffer layer is excellent in lowering the interfacial resistance between the positive electrode active material and the solid electrolyte particles while improving the performance of the positive electrode active material by facilitating the movement of lithium ions and electron conduction. The buffer layer may be amorphous. That is, the lithium compound and the metal oxide in the buffer layer may be amorphous. When the amorphous compound is formed as a buffer layer on the surface of the positive electrode active material, the interfacial resistance between the positive electrode active material and the solid electrolyte particles can be lowered without impairing the performance of the positive electrode active material, thereby improving the capacity characteristics and life characteristics of the all-solid-state secondary battery.

The thickness of the buffer layer may be approximately 1 nm to 20 nm, for example 2 nm to 15 nm, or 5 nm to 10 nm. The buffer layer is formed with such a very thin thickness that it can effectively reduce the interfacial resistance between solid particles without impairing the performance of the positive electrode active material.

양극 활물질의 제조 방법Method for manufacturing positive electrode active material

In one embodiment, a method for producing a cathode active material is provided, comprising: mixing an organic material and a lithium salt to produce a composite; mixing the composite with cathode active material particles including a lithium transition metal composite oxide; and drying the composite to coat the surface of the cathode active material particles with the composite, wherein the organic material comprises a (meth)acrylate containing an alkylene glycol unit, an ether containing an alkylene glycol unit, or a combination thereof. The coated cathode active material described above can be produced using this method.

Since the organic matter, lithium salt, and positive electrode active material particles have been described above, a detailed description thereof will be omitted.

The organic material may be mixed in an amount of 0.05 to 5 parts by weight with respect to 100 parts by weight of the positive electrode active material particles, for example, 0.05 to 4 parts by weight, 0.1 to 3 parts by weight, or 0.5 to 2 parts by weight.

In addition, the lithium salt may be mixed in an amount of 0.05 parts by weight to 5 parts by weight per 100 parts by weight of the positive electrode active material particles, for example, 0.05 parts by weight to 4 parts by weight, 0.1 parts by weight to 3 parts by weight, or 0.5 parts by weight to 2 parts by weight.

The weight ratio of the organic material and the lithium salt may be from 2:8 to 9:1, for example, from 2:8 to 8:2, from 3:7 to 7:3, or from 2:8 to 6:4. The drying may be performed at a temperature range of from 60° C. to 150° C. and for from 1 hour to 48 hours.

The coating process according to one embodiment may be a wet coating method or a solid coating method. For example, coating may be performed by dissolving the organic material and the lithium salt in a solvent, adding the positive electrode active material particles, mixing, and then drying. By applying the wet coating method, a thin and uniform coating layer may be formed. Alternatively, the positive electrode active material particles, the organic material, and the lithium salt may be mixed without a solvent, for example, in a sink mixer. If the solid coating method is applied, a coating layer of an appropriate thickness may be formed without damaging the positive electrode active material.

전고체 이차 전지용 양극Cathode for all-solid-state secondary battery

In one embodiment, a positive electrode for an all-solid-state secondary battery is provided, including the above-described positive electrode active material, and a sulfide-based solid electrolyte. Specifically, the positive electrode according to one embodiment includes a current collector, and a positive electrode active material layer positioned on the current collector, wherein the positive electrode active material layer includes the above-described positive electrode active material and the sulfide-based solid electrolyte, and may optionally include a conductive material and/or a binder. The above-described positive electrode active material has a coating layer formed on a surface including a specific organic material and a lithium salt, wherein the coating layer has high oxidation resistance, high adhesiveness, and high lithium ion conductivity while being non-reactive with the sulfide-based solid electrolyte, and is therefore suitable for application to a positive electrode of an all-solid-state secondary battery applying a sulfide-based solid electrolyte.

Sulfide solid electrolyte

The above sulfide-based solid electrolyte is, for example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ --LiX (X is a halogen element, for example, I or Cl), Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (m and n are each integers, and Z is Ge, Zn, or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ It may include PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or combinations thereof.

Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li ₂ S and P ₂ S ₅ in a molar ratio of 50:50 to 90:10, or a molar ratio of 50:50 to 80:20, and optionally performing a heat treatment. In the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, other components such as SiS ₂ , GeS ₂ , and B ₂ S ₃ can be further included to further improve the ionic conductivity.

As a method of mixing sulfur-containing raw materials for producing a sulfide-based solid electrolyte, mechanical milling or a solution method can be applied. Mechanical milling is a method of putting starting raw materials in a ball mill reactor, vigorously stirring them, and mixing them by pulverizing them. When using a solution method, the starting raw materials can be mixed in a solvent to obtain a solid electrolyte as a precipitate. In addition, if heat treatment is performed after mixing, the crystals of the solid electrolyte can become more solid and the ionic conductivity can be improved. For example, a sulfide-based solid electrolyte can be produced by mixing sulfur-containing raw materials and performing heat treatment twice or more, in which case a sulfide-based solid electrolyte with high ionic conductivity and solidity can be produced.

According to one embodiment, a sulfide-based solid electrolyte can be manufactured through, for example, a first heat treatment of mixing sulfur-containing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the results of the first heat treatment and calcining at 350°C to 800°C. The first heat treatment and the second heat treatment can each be performed in an inert gas or nitrogen atmosphere. The first heat treatment can be performed for 1 hour to 10 hours, and the second heat treatment can be performed for 5 hours to 20 hours. The first heat treatment can have the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and durability can be obtained, and such a solid electrolyte can be said to be suitable for mass production. The temperature of the first heat treatment may be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of the second heat treatment may be, for example, 380°C to 700°C, or 400°C to 600°C.

For example, the sulfide-based solid electrolyte may include an argyrodite-type sulfide. The argyrodite-type sulfide may be represented by a chemical formula of, for example, Li _a M _b P _c S _d A _e (wherein a, b, c, d, and e are all 0 or more and 12 or less, M is Ge, Sn, Si, or a combination thereof, and A is F, Cl, Br, or I), and as a specific example, may be represented by a chemical formula of Li _7-x PS _6-x A _x (wherein x is 0.2 or more and 1.8 or less, and A is F, Cl, Br, or I). The above argyrodite-type sulfides may specifically be Li ₃ PS ₄ , Li ₇ P ₃ S ₁₁ , Li ₇ PS ₆ , Li ₆ PS ₅ Cl, Li ₆ PS ₅ Br, Li _5.8 PS _4.8 Cl _1.2 , Li _6.2 PS _5.2 Br _0.8 , etc.

The sulfide-based solid electrolyte including such argyrodite-type sulfides has a high ionic conductivity close to the ionic conductivity of a typical liquid electrolyte at room temperature, which is in the range of 10 ^-4 to 10 ^-2 S/cm, and can form a close bond between a cathode active material and a solid electrolyte without causing a decrease in ionic conductivity, and further can form a close interface between an electrode layer and a solid electrolyte layer. An all-solid-state secondary battery including the same can have improved battery performances, such as rate characteristics, Coulombic efficiency, and cycle life characteristics.

The argyrodite-type sulfide-based solid electrolyte can be manufactured by, for example, mixing lithium sulfide and phosphorus sulfide, and optionally lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing the argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120° C. to 350° C., and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350° C. to 800° C.

The average particle diameter (D50) of the above-mentioned sulfide-based solid electrolyte particles may be, for example, 0.1 ㎛ to 5.0 ㎛, and may be small particles of 0.1 ㎛ to 1.9 ㎛, or large particles of 2.0 ㎛ to 5.0 ㎛. For example, the average particle diameter (D50) of the sulfide-based solid electrolyte included in the positive electrode may be about 0.1 ㎛ to 1.9 ㎛, which may be smaller than the average particle diameter of the solid electrolyte included in the solid electrolyte layer. The solid electrolyte satisfying the above-mentioned average particle diameter range can effectively penetrate between positive electrode active materials, and has excellent contactability with the positive electrode active material and excellent connectivity between the solid electrolyte particles. Here, the average particle diameter may be measured by an electron microscope image, and for example, the particle size distribution may be obtained by measuring the sizes (diameter or major axis length) of about 20 particles in a scanning electron microscope image, and the D50 may be calculated from this.

With respect to the total weight of the positive electrode active material layer, the solid electrolyte may be included in an amount of 0.1 wt% to 35 wt%, for example, 1 wt% to 35 wt%, 5 wt% to 30 wt%, 8 wt% to 25 wt%, or 10 wt% to 20 wt%.

In addition, in the positive electrode active material layer, the positive electrode active material may be included in an amount of 65 wt% to 99 wt% and the solid electrolyte in an amount of 1 wt% to 35 wt% based on the total weight of the positive electrode active material and the solid electrolyte, for example, the positive electrode active material may be included in an amount of 80 wt% to 90 wt% and the solid electrolyte in an amount of 10 wt% to 20 wt%. When the solid electrolyte is included in the positive electrode in such an amount, the efficiency and life characteristics of the all-solid-state battery can be improved without reducing the capacity.

Challenge

The conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change in the battery to be formed and is electronically conductive can be used. Examples of such conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials containing copper, nickel, aluminum, silver, etc. and in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

The content of the conductive material in the above positive electrode active material layer may be 0.1 wt% to 5 wt% with respect to the total weight of the positive electrode active material layer.

bookbinder

According to one embodiment, the positive electrode can realize excellent adhesion between solid particles without using a separate binder by including the aforementioned positive electrode active material coated with an organic material. In particular, the fluorine-based binder can limit the movement of lithium in the positive electrode in an all-solid-state secondary battery, and in one embodiment, excellent adhesion can be realized even without including the fluorine-based binder. In other words, the positive electrode for an all-solid-state secondary battery according to one embodiment can be said to be a positive electrode that does not include a fluorine-based binder.

However, the anode may further include various binders as needed. The binder may be, for example, a polymer including polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, ethylene oxide, polyvinyl pyrrolidone, polyurethane, polyethylene, polypropylene, polyalkyl (meth)acrylate, styrene-butadiene rubber, acrylated styrene-butadiene rubber, nitrile-butadiene rubber, hydrogenated nitrile-butadiene rubber, acrylic rubber, natural rubber, epoxy resin, nylon, etc.

The content of the binder in the above positive electrode active material layer may be approximately 0.1 wt% to 5 wt% with respect to the total weight of the positive electrode active material layer.

As the above positive electrode collector, aluminum foil or stainless steel foil such as SUS can be used, but is not limited thereto.

전고체 이차 전지All-solid-state secondary battery

In one embodiment, an all-solid-state secondary battery is provided, which includes the aforementioned positive and negative electrodes and a solid electrolyte layer positioned between the positive and negative electrodes. The all-solid-state secondary battery may be expressed as an all-solid-state battery, an all-solid-state lithium secondary battery, etc.

FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 1, an all-solid-state secondary battery (100) may have a structure in which an electrode assembly in which an anode (400) including an anode current collector (401) and an anode active material layer (403), a solid electrolyte layer (300), and a cathode (200) including an anode active material layer (203) and a cathode current collector (201) are laminated is housed in a case such as a pouch. The all-solid-state secondary battery (100) may further include an elastic layer (500) on the outer side of at least one of the cathode (200) and the anode (400). Although FIG. 1 illustrates one electrode assembly including an anode (400), a solid electrolyte layer (300), and a cathode (200), an all-solid-state secondary battery may be manufactured by laminating two or more electrode assemblies.

음극cathode

An anode for an all-solid-state secondary battery includes a current collector and a negative electrode active material layer positioned on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and/or a conductive material.

The above negative active material includes a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

As the above lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiO _x (0 < x < 2), a Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but is not Si), and as the Sn-based negative electrode active material, Sn, SnO ₂ , a Sn-R alloy (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but is not Sn), and the like. In addition, at least one of these and SiO ₂ can be mixed and used. The above elements Q and R may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

For example, the negative active material may include silicon-carbon composite particles. The average particle diameter (D50) of the silicon-carbon composite particles may be, for example, 0.5 ㎛ to 20 ㎛. The average particle diameter (D50) is measured by a particle size analyzer and refers to the diameter of particles having a cumulative volume of 50 volume% in a particle size distribution. With respect to 100 wt% of the silicon-carbon composite particles, silicon may be included in an amount of 10 wt% to 60 wt% and carbon may be included in an amount of 40 wt% to 90 wt%. The silicon-carbon composite particles may include, for example, a core including silicon particles, and a carbon coating layer positioned on a surface of the core. The average particle diameter (D50) of the silicon particles in the core may be 10 nm to 1 ㎛, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented as SiO _x (0<x<2). Additionally, the thickness of the carbon coating layer can be about 5 nm to 100 nm.

For example, the silicon-carbon composite particle may include a core including silicon particles and crystalline carbon, and a carbon coating layer positioned on the surface of the core and including amorphous carbon. For example, in the silicon-carbon composite particle, the amorphous carbon may not be present in the core but may be present only in the carbon coating layer. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof, and the amorphous carbon may be formed from coal pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, or a polymer resin (phenol resin, furan resin, polyimide resin, etc.). At this time, the content of the crystalline carbon may be 10 wt% to 70 wt% with respect to 100 wt% of the silicon-carbon composite particle, and the content of the amorphous carbon may be 20 wt% to 40 wt%.

In the above silicon-carbon composite particle, the core may include a void in the central portion. The radius of the void may be 30% to 50% of the radius of the silicon-carbon composite particle.

The silicon-carbon composite particles described above can effectively suppress problems such as volume expansion, structural collapse, or particle crushing due to charge and discharge, thereby preventing the phenomenon of conductive path disconnection, realizing high capacity and high efficiency, and are advantageous for use under high voltage or high-speed charging conditions.

The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in a mixture, the mixing ratio can be 1:99 to 90:10 by weight.

The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative active material layer.

In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% with respect to the total weight of the negative electrode active material layer. In addition, when the negative electrode active material layer further includes a conductive material, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

The above binder serves to adhere the negative active material particles well to each other and also to adhere the negative active material well to the current collector. The binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

The above-mentioned insoluble binders may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymers, polystyrene, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide or combinations thereof.

The above water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound that can provide viscosity as a kind of thickener may be further included. As the cellulose-based compound, one or more types of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. The amount of such thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change in the battery to be formed and is electronically conductive can be used. Examples of such conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials including copper, nickel, aluminum, and silver in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

As another example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode. The precipitation-type negative electrode may mean a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this serves as a negative electrode active material.

FIG. 2 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation-type negative electrode. Referring to FIG. 2, the precipitation-type negative electrode (400') may include a current collector (401) and a negative electrode coating layer (405) positioned on the current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material exists, and when charging, high-density lithium metal is precipitated or deposited between the current collector (401) and the negative electrode coating layer (405) or on the negative electrode coating layer (405) to form a lithium metal layer (404), which may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) positioned on the current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

The above cathode coating layer (405) may be called a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a metal, carbon material, or a combination thereof that acts as a catalyst.

The metal may be a lithium-philic metal, and may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one kind of these or may be composed of several kinds of alloys. When the metal is present in the form of particles, the average particle diameter (D50) thereof may be about 4 μm or less, for example, 10 nm to 4 μm.

The carbon material can be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon can be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon can be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

When the above-described negative electrode coating layer (405) includes both the metal and the carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The above-described negative electrode coating layer (405) may include, for example, a carbon material supported with a catalytic metal, or may include a mixture of metal particles and carbon material particles.

The above-described cathode coating layer (405) may include, for example, the above-described lithium-philic metal and amorphous carbon, in which case the precipitation of lithium metal may be effectively promoted. As a specific example, the above-described cathode coating layer (405) may include a composite in which a lithium-philic metal is supported on amorphous carbon.

The above cathode coating layer (405) may further include a binder, and the binder may be, for example, a conductive binder. In addition, the above cathode coating layer (405) may further include general additives such as fillers, dispersants, and ion conductive agents.

The thickness of the cathode coating layer (405) may be, for example, 100 nm to 20 ㎛, or 500 nm to 10 ㎛, or 1 ㎛ to 5 ㎛.

The above-described precipitated negative electrode (400') may further include, for example, a thin film on the surface of the current collector, that is, between the current collector and the negative electrode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one type of these or may be composed of multiple types of alloys. The thin film may further flatten the precipitated form of the lithium metal layer (404) and further improve the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like. The thickness of the thin film may be, for example, 1 nm to 500 nm.

The above lithium metal layer (404) may include lithium metal or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

The thickness of the lithium metal layer (404) may be 1 ㎛ to 500 ㎛, 1 ㎛ to 200 ㎛, 1 ㎛ to 100 ㎛, or 1 ㎛ to 50 ㎛. If the thickness of the lithium metal layer (404) is too thin, it may be difficult to perform the role of a lithium storage, and if it is too thick, the battery volume may increase and the performance may deteriorate.

When such a precipitation-type cathode is applied, the cathode coating layer (405) can play a role in protecting the lithium metal layer (404) and suppressing the precipitation growth of lithium dendrites. Accordingly, short-circuiting and capacity reduction of the all-solid-state battery can be suppressed, and the life characteristics can be improved.

고체 전해질 층Solid electrolyte layer

The solid electrolyte layer (300) may include solid electrolyte particles and optionally a binder. The solid electrolyte particles may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, etc. Since the sulfide-based solid electrolyte is as described above, a detailed description thereof will be omitted.

The above oxide-based solid electrolytes include, for example, Li _1+x Ti _2-x Al(PO ₄ ) ₃ (LTAP)(0≤x≤4), Li _1+x+y Al _x Ti _2-x Si _y P _3-y O ₁₂ (0<x<2, 0≤y<3), BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT)(0≤x<1, 0≤y<1), PB(Mg ₃ Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , Na ₂ O, MgO, NiO, CaO, BaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), Li _1+x+y (Al, Ga) _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), Li ₂ O, LiAlO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ system ceramics, garnet system ceramics Li _3+x La ₃ M ₂ O ₁₂ (M = Ta, Te, Nb, Zr, or a combination thereof; x is 1 to 10). ), or mixtures thereof.

Meanwhile, the average particle diameter (D50) of the solid electrolyte included in the solid electrolyte layer (300) may be larger than the average particle diameter (D50) of the solid electrolyte included in the positive electrode (200). In this case, the energy density of the all-solid-state secondary battery may be maximized while increasing the mobility of lithium ions, thereby improving the overall performance. For example, the average particle diameter (D50) of the solid electrolyte included in the positive electrode (200) may be 0.1 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D50) of the solid electrolyte included in the solid electrolyte layer (300) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When the above particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized while the transport of lithium ions is facilitated, thereby suppressing the resistance and improving the overall performance of the all-solid-state secondary battery. Here, the average particle size (D50) of the solid electrolyte can be measured by a particle size analyzer using laser diffraction.

The above solid electrolyte layer may further include a binder in addition to the solid electrolyte particles. At this time, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate polymer, or a combination thereof, but is not limited thereto, and any binder used in the relevant technical field may be used. The acrylate polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

The above solid electrolyte layer can be formed by adding a solid electrolyte to a binder solution, coating it on a base film, and drying it. The solvent of the binder solution can be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer forming process is widely known in the art, a detailed description thereof will be omitted.

The thickness of the solid electrolyte layer may be, for example, 10 ㎛ to 150 ㎛.

The above solid electrolyte layer may further include an alkali metal salt, and/or an ionic liquid, and/or a conductive polymer.

The above alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt may improve ion conductivity by enhancing lithium ion mobility of the solid electrolyte layer.

The lithium salt may include, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiPO ₂ F ₂ , LiCl, LiI, LiSCN, LiN(CN) ₂ , lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, or a combination thereof.

For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. The imide-based lithium salt can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

The above ionic liquid has a melting point below room temperature and is a salt or room-temperature molten salt that is liquid at room temperature and consists only of ions.

The above ionic liquid comprises a) at least one cation selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof, and b) BF ₄ ^- , PF ₆ ^- , AsF ₆ ^- , SbF ₆ ^- , AlCl ₄ ^- , HSO ₄ ^- , ClO ₄ ^- , CH ₃ SO ₃ ^- , CF ₃ CO ₂ ^- , Cl ^- , Br ^- , I ^- , BF ₄ ^- , SO ₄ ^- , CF ₃ SO ₃ ^- , (FSO ₂ ) ₂ N ^- , (C ₂ F ₅ SO ₂ ) ₂ N ^- , (C ₂ F ₅ SO ₂ )(CF ₃ SO ₂ )N ^- , and (CF ₃ SO ₂ ) ₂ N ^- may be a compound including at least one anion selected from the group consisting of:

The above ionic liquid may be at least one selected from the group consisting of, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

In the above solid electrolyte layer, the weight ratio of the solid electrolyte and the ionic liquid can be 0.1:99.9 to 90:10, and for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. The solid electrolyte layer satisfying the above range can improve the electrochemical contact area with the electrode, thereby maintaining or improving the ionic conductivity. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

The above-mentioned all-solid-state secondary battery may be a unit cell having a structure of positive electrode/solid electrolyte layer/negative electrode, a bicell having a structure of negative electrode/solid electrolyte layer/positive electrode/solid electrolyte layer/negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-sized batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state secondary battery can be used in hybrid vehicles, such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields that require a large amount of power storage, and for example, it can be used in electric bicycles or power tools. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields, such as portable electronic devices.

Hereinafter, examples and comparative examples of the present invention will be described. The following examples are only examples of the present invention, and the present invention is not limited to the following examples.

실시예 1Example 1

1. Manufacturing of positive electrode active material

The cathode active material particles were prepared _by mixing small particles _with an average particle size of about 4 ㎛ and large particles with an average particle size of about 18 ㎛ in a weight ratio of 3:7, with a composition of LiNi _0.944 Co _0.04 _Al 0.012 Mn 0.004 O 2 and a buffer layer of lithium zirconium oxide formed thereon.

In a diethyl carbonate (DEC) solvent, 0.5 parts by weight of poly(ethylene glycol) diacrylate (PEGDA) having a number average molecular weight of approximately 700 g/mol and 0.75 parts by weight of LiTFSI were mixed, and then 100 parts by weight of the prepared cathode active material particles were added and mixed. After removing the solvent, the mixture was dried at 60°C for 5 min and then vacuum-dried at 80°C for 2 hours, thereby producing a coated cathode active material.

2. Manufacturing of the anode

In an octyl acetate solvent, 85 wt% of the manufactured coated positive electrode active material, 13.5 wt% of sulfide-based solid electrolyte particles (Li ₆ PS ₅ Cl, D50 = 0.85 μm), 1.0 wt% of an acrylic binder, and 0.5 wt% of a carbon nanotube conductive material were mixed to prepare a positive electrode composition. This was applied onto a SUS current collector using a bar coater, and then rolled and dried to prepare a positive electrode.

3. Manufacturing of the cathode

An Ag/C composite was prepared by mixing carbon black having a primary particle size (D50) of about 30 nm and silver (Ag) having an average particle size (D50) of about 60 nm in a weight ratio of 3:1, and 0.25 g of the composite was added to 2 g of an NMP solution containing 7 wt% of polyvinylidene fluoride binder and mixed to prepare a negative electrode coating layer composition. This was applied to a nickel foil current collector using a bar coater and vacuum-dried to prepare a deposition-type negative electrode in which a negative electrode coating layer was formed on the current collector.

4. Preparation of solid electrolyte layer

A composition for forming a solid electrolyte layer was prepared by adding and mixing a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl, D50=3 μm) and an organic dispersant to an IBIB solvent containing an acrylic binder. The composition includes 98.7 wt% of a sulfide-based solid electrolyte, 1.0 wt% of a binder, and 0.3 wt% of an organic dispersant. The composition is cast on a release PET film and dried at room temperature to prepare a solid electrolyte layer.

5. Manufacturing of all-solid-state secondary batteries

After laminating the positive electrode, solid electrolyte layer, and negative electrode in that order, it was sealed in a pouch shape and subjected to hydrostatic pressing at a high temperature of 80°C and 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

비교예 1Comparative Example 1

Except that a positive electrode active material having a composition of LiNi _0.944 Co _0.04 Al _0.012 Mn _0.004 O ₂ and a buffer layer of lithium zirconium oxide was formed, and a mixture of small particles having an average particle size of about 4 ㎛ and large particles having an average particle size of about 18 ㎛ was used in a weight ratio of 3:7, without performing coating with an organic material and a lithium salt, a positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

비교예 2Comparative Example 2

A method of adding PEGDA and LiTFSI to the positive electrode composition was applied without coating the positive electrode active material particles with PEGDA and LiTFSI. That is, 85 wt% of the positive electrode active material of Comparative Example 1, 13.5 wt% of sulfide-based solid electrolyte particles (Li ₆ PS ₅ Cl, D50 = 0.85 μm), 1.0 wt% of an acrylic binder, and 0.5 wt% of a carbon nanotube conductive material were mixed in an octyl acetate solvent, wherein 0.5 wt% of PEGDA and 0.75 wt% of LiTFSI were added with respect to 100 wt% of the positive electrode active material and mixed together, thereby preparing a positive electrode composition according to Comparative Example 2. This was applied on a current collector with a bar coater, and then rolled and dried to prepare a positive electrode. Thereafter, substantially the same method as in Example 1 was applied to manufacture an all-solid-state secondary battery.

비교예 3Comparative Example 3

A cathode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that polyethylene glycol (PEG) having a weight average molecular weight of 1,000 g/mol was used instead of PEGDA.

비교예 4Comparative Example 4

A cathode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that ethylhexyl acrylate having a weight-average molecular weight of 4,000 g/mol was used instead of PEGDA.

평가예: 수명 특성 평가Evaluation Example: Life Characteristics Evaluation

For the batteries manufactured in Example 1 and Comparative Examples 1 and 2, the batteries were charged at a constant current of 0.1 C at 45°C to an upper limit voltage of 4.25 V and a constant voltage of 0.05 C, and then discharged at 0.1 C to an end-of-discharge voltage of 2.5 V to perform an initial charge/discharge. Thereafter, the cycle of charging at 0.33 C and discharging at 0.33 C in a voltage range of 2.5 V to 4.25 V at 45°C was repeated 100 times to evaluate the life characteristics. FIG. 3 shows the discharge capacity according to the number of cycles, and FIG. 4 shows the capacity retention rate according to the number of cycles. The capacity retention rate means the ratio of the discharge capacity in each cycle to the discharge capacity in the first cycle, and the unit is %.

Referring to FIG. 3, it can be confirmed that the discharge capacities of Example 1 and Comparative Example 1 are reversed around the 50th cycle, and that the discharge capacity of Example 1 is higher than that of Comparative Example 1 after the 50th cycle. Referring to FIG. 4, it can be seen that the capacity retention rate of Example 1 is higher than that of Comparative Examples 1 and 2 throughout the cycle.

Meanwhile, in the case of Comparative Example 3, it was confirmed that PEG was reactive with the sulfide-based solid electrolyte, thereby increasing the resistance of the battery, and in the case of Comparative Example 4, it was confirmed that the first coulombic efficiency of the battery decreased and the life characteristics also deteriorated due to the oxidation resistance problem of the acrylic system.

Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[Explanation of symbols]

100: All-solid-state battery 200: Cathode

201: Cathode current collector 203: Cathode active material layer

300: solid electrolyte layer 400: cathode

401: Negative electrode current collector 403: Negative electrode active material layer

400’: precipitation type cathode 404: lithium metal layer

405: Negative coating layer 500: Elastic layer

Claims

A cathode active material particle comprising a lithium transition metal composite oxide, and

Comprising a coating layer positioned on the surface of the above positive electrode active material particles,

The above coating layer contains organic matter and lithium salt,

A cathode active material, wherein the organic material comprises a (meth)acrylate containing an alkylene glycol unit, an ether containing an alkylene glycol unit, or a combination thereof.
In paragraph 1,

The above alkylene glycol is a positive electrode active material which is ethylene glycol, propylene glycol, or neopentyl glycol.
In paragraph 1,

The (meth)acrylate containing the above alkylene glycol unit, the ether containing the alkylene glycol unit, or a combination thereof is selected from the group consisting of poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) monoacrylate (PEGMA), poly(propylene glycol) diacrylate (PPGDA), poly(propylene glycol) dimethacrylate (PPGDMA), di(ethylene glycol) diacrylate (DEGDA), tri(ethylene glycol) diacrylate (TEGDA), tetra(ethylene glycol) diacrylate (TTEGDA), di(propylene glycol) diacrylate (DPGDA), tri(propylene glycol) diacrylate (TPGDA), ethoxylated trimethylolpropane triacrylate (ETPTA), poly(ethylene glycol) methyl ether methacrylate (PEGDMA), poly(ethylene glycol) dimethyl ether (PEGDME; polyglime), A cathode active material comprising tri(ethylene glycol) dimethyl ether (triglyme), tetra(ethylene glycol) dimethyl ether (TEGDME, tetraglyme), or a combination thereof.
In paragraph 1,

A cathode active material comprising a (meth)acrylate containing the alkylene glycol unit, an ether containing the alkylene glycol unit, or a combination thereof, wherein the cathode active material comprises poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) monoacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (PEGDMA), poly(ethylene glycol) dimethyl ether (PEGDME; polyglime), or a combination thereof.
In paragraph 1,

A cathode active material, wherein the (meth)acrylate containing the alkylene glycol unit and the ether containing the alkylene glycol unit each independently have a number average molecular weight of 200 g/mol to 2,000 g/mol.
In paragraph 1,

A cathode active material, wherein the organic material is contained in an amount of 20 to 90 wt% and the lithium salt is contained in an amount of 10 to 80 wt% based on 100 wt% of the total of the organic material and the lithium salt in the coating layer.
In paragraph 1,

A cathode active material having a total content of the organic material and lithium salt of 0.1 to 10 parts by weight based on 100 parts by weight of the cathode active material particles.
In paragraph 1,

A cathode active material, wherein the organic material is contained in an amount of 0.05 to 5 wt%, and the lithium salt is contained in an amount of 0.05 to 5 wt%, based on 100 wt% of the cathode active material.
In paragraph 1,

The above lithium salt is a cathode active material including LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiPO 2 F 2 , LiCl, LiI, LiSCN, LiN(CN) 2 , lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, or a combination thereof.
In paragraph 1,

The above coating layer is a positive electrode active material that exists in the form of an island or a continuous film on the surface of the positive electrode active material particles.
In paragraph 1,

A cathode active material having a thickness of the coating layer of 1 nm to 50 nm.
In paragraph 1,

The above lithium transition metal composite oxide is a positive electrode active material which is a lithium nickel-based oxide represented by the following chemical formula 1, a lithium cobalt-based oxide represented by the following chemical formula 2, a lithium iron phosphate-based compound represented by the following chemical formula 3, or a cobalt-free lithium nickel-manganese-based oxide represented by the following chemical formula 4:

[Chemical Formula 1]

Li a1 Ni x1 M 1 y1 M 2 z1 O 2- b1

In the chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, M 1 and M 2 are each independently at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, X is at least one element selected from the group consisting of F, P, and S,

[Chemical formula 2]

Li a2 Co x2 M 3 y2 O 2- b2

In the chemical formula 2, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, M 3 is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, X is at least one element selected from the group consisting of F, P, and S,

[Chemical Formula 3]

Li a3 Fe x3 M 4 y3 PO 4- b3

In the chemical formula 3, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, M 4 is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, X is at least one element selected from the group consisting of F, P, and S,

[Chemical Formula 4]

Li a4 Ni x4 Mn y4 M 5 z4 O 2- b4

In the chemical formula 4, 0.9≤a4≤1.8, 0.8≤x4<1, 0<y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, and 0≤b4≤0.1, and M 5 is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is at least one element selected from the group consisting of F, P, and S.
In Article 12,

The above lithium transition metal composite oxide is a lithium nickel-based oxide represented by the above chemical formula 1, and is a cathode active material that is a high nickel-based oxide satisfying 0.8≤x1<1, 0<y1≤0.2, and 0≤z1≤0.2.
In Article 13,

The above lithium transition metal composite oxide is a lithium nickel-based oxide represented by the above chemical formula 1, and is a cathode active material that is a high nickel-based oxide satisfying 0.9≤x1<1, 0<y1≤0.1, and 0≤z1≤0.1.
In paragraph 1,

A cathode active material having an average particle diameter (D50) of 1 ㎛ to 25 ㎛.
In paragraph 1,

The above cathode active material particles include small particles having an average particle diameter (D50) of 1 ㎛ to 9 ㎛ and large particles having an average particle diameter (D50) of 10 ㎛ to 20 ㎛.
In Article 16,

A cathode active material, wherein the small particles are contained in an amount of 5 to 40 wt% and the opposing particles are contained in an amount of 60 to 95 wt%, based on 100 wt% of the total of the small particles and the opposing particles.
In Article 16,

The above particles and antiparticles are positive active materials in the form of secondary particles in which a plurality of primary particles are aggregated.
In Article 16,

The above-mentioned small particles are in the form of single particles, and the above-mentioned large particles are in the form of secondary particles in which a plurality of primary particles are aggregated.
In paragraph 1,

The above cathode active material further includes a buffer layer between the cathode active material particles and the coating layer,

A cathode active material, wherein the buffer layer comprises a lithium compound and a metal oxide, and the metal is at least one selected from Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr.
A method of manufacturing a composite by mixing an organic material and a lithium salt, mixing the composite with a cathode active material particle including a lithium transition metal composite oxide, and drying the composite to coat the surface of the cathode active material particle with the composite,

A method for producing a positive electrode active material, wherein the organic material comprises a (meth)acrylate containing an alkylene glycol unit, an ether containing an alkylene glycol unit, or a combination thereof.
In Article 21,

A method for producing a positive electrode active material, wherein the organic material is mixed in an amount of 0.05 to 5 parts by weight and the lithium salt is mixed in an amount of 0.05 to 5 parts by weight relative to 100 parts by weight of the positive electrode active material particles.
In Article 21,

A method for producing a cathode active material, wherein the organic material and the lithium salt are mixed in a weight ratio of 2:8 to 9:1.
In Article 21,

A method for producing a positive electrode active material, wherein the above drying is performed at a temperature range of 60°C to 150°C.
A positive electrode for an all-solid-state secondary battery comprising a positive electrode active material according to any one of claims 1 to 20, and a sulfide-based solid electrolyte.
In Article 25,

The above sulfide-based solid electrolyte is a positive electrode for an all-solid-state secondary battery containing an argyrodite-type sulfide.
In Article 25,

A positive electrode for an all-solid-state secondary battery, wherein the above-mentioned sulfide-based solid electrolyte is in the form of particles and has an average particle diameter (D50) of 0.1 ㎛ to 1.9 ㎛.
In Article 25,

An all-solid-state secondary battery positive electrode, wherein the positive electrode active material is contained in an amount of 65 to 99 wt%, and the sulfide-based solid electrolyte is contained in an amount of 1 to 35 wt%, based on 100 wt% of the total amount of the positive electrode active material and the sulfide-based solid electrolyte.
In Article 25,

The above anode further comprises a conductive material,

The above-mentioned challenge material is a cathode for an all-solid-state secondary battery comprising natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanofibers, carbon nanotubes, or a combination thereof.
In Article 25,

The above positive electrode is an all-solid-state secondary battery positive electrode that does not contain a fluorine-based binder.
The anode according to Article 25,

Cathode and

An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive and negative electrodes.
In Article 31,

The above negative electrode comprises a current collector and a negative electrode coating layer positioned on the current collector and containing a lithium-philic metal, a carbon material, or a combination thereof,

An all-solid-state secondary battery comprising a lithium metal layer formed by charging between the above-described collector and the negative electrode coating layer.