Composite positive electrode for all-solid-state lithium secondary battery and all-solid-state lithium secondary battery comprising same

Abstract

The present invention provides a composite positive electrode for an all-solid-state lithium secondary battery and an all-solid-state lithium secondary battery including the same, the composite positive electrode for an all-solid-state lithium secondary battery including a sulfide-based solid electrolyte and a positive electrode binder including a non-aromatic hydrocarbon butadiene rubber and a fluorine-based rubber.

Description

Technical Field

[0001] The present invention relates to a composite positive electrode for an all-solid-state lithium secondary battery and an all-solid-state lithium secondary battery comprising the composite positive electrode. Background Art

[0002] In recent years, with increasing concern about environmental issues, exhaust emissions from vehicles using fossil fuels such as gasoline and diesel have been identified as a major cause of air pollution. As an alternative to these, extensive research is underway into electric vehicles (EVs) and hybrid electric vehicles (HEVs). Furthermore, lithium secondary batteries, which offer high discharge voltage and stable power, are primarily used as power sources for these EVs and HEVs.

[0003] On the other hand, existing lithium secondary batteries using liquid electrolytes have the risk of fire due to leakage of the liquid electrolyte, and there are problems such as secondary battery swelling caused by electrolyte decomposition caused by electrode reactions. Therefore, in recent years, in order to solve the above problems, all-solid-state lithium secondary batteries using solid electrolytes have been actively researched and developed. Summary of the Invention

[0004] (1) Technical issues to be resolved

[0005] An object of one embodiment of the present invention is to provide a composite cathode having improved ionic conductivity of a solid electrolyte.

[0006] Another embodiment of the present invention aims to improve the initial discharge capacity of an all-solid-state lithium secondary battery.

[0007] (2) Technical solution

[0008] One aspect of the present invention provides a composite positive electrode for an all-solid-state lithium secondary battery, comprising: a sulfide-based solid electrolyte; and a positive electrode binder, wherein the positive electrode binder comprises non-aromatic hydrocarbon-based butadiene rubber and fluorine-based rubber.

[0009] The non-aromatic hydrocarbon-based butadiene rubber may include butadiene rubber (BR).

[0010] The fluorine-based rubber may include at least one of polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0011] The sulfide-based solid electrolyte may be of argyrodite type.

[0012] The positive electrode binder may include the non-aromatic hydrocarbon-based butadiene and the fluorine-based rubber in a weight ratio of 1:99 to 99:1.

[0013] The non-aromatic hydrocarbon-based butadiene rubber may have a weight average molecular weight of about 590,000 to about 720,000.

[0014] The fluorine-based rubber may have a weight average molecular weight of 100,000 to 600,000.

[0015] The composite positive electrode for an all-solid-state lithium secondary battery may further include a positive electrode conductive material. The composite positive electrode for an all-solid-state lithium secondary battery may include the positive electrode conductive material and the positive electrode binder in a weight ratio of 1:99 to 99:1.

[0016] The sulfide-based solid electrolyte may be of an argyrodite type, and the positive electrode binder may include butadiene rubber and fluorine-based rubber.

[0017] The fluorine-based rubber may include at least one of polyvinylidene fluoride, polyhexafluoropropylene, and polyvinylidene fluoride-hexafluoropropylene.

[0018] The sulfide-based solid electrolyte may be of argyrodite type, the positive electrode binder may include a positive electrode binder comprising non-aromatic hydrocarbon-based butadiene rubber and fluorine-based rubber, and the fluorine-based rubber may include at least one of polyvinylidene fluoride, polyhexafluoropropylene, and polyvinylidene fluoride-hexafluoropropylene.

[0019] The non-aromatic hydrocarbon-based butadiene rubber may include butadiene rubber.

[0020] Another aspect of the present invention provides an all-solid-state lithium secondary battery, which includes: a composite positive electrode, the composite positive electrode including a sulfide-based solid electrolyte and a positive electrode binder, the positive electrode binder including non-aromatic hydrocarbon butadiene rubber and fluorine-based rubber; and a solid electrolyte layer, the solid electrolyte layer being arranged on at least one side of the composite positive electrode.

[0021] The non-aromatic hydrocarbon-based butadiene rubber may include butadiene rubber.

[0022] The fluorine-based rubber may include at least one of polyvinylidene fluoride, polyhexafluoropropylene, and polyvinylidene fluoride-hexafluoropropylene.

[0023] The sulfide-based solid electrolyte may be of argyrodite type.

[0024] The sulfide-based solid electrolyte of the solid electrolyte layer and the sulfide-based solid electrolyte of the composite positive electrode may be of argyrodite type.

[0025] The all-solid-state lithium secondary battery may further include a lithium metal negative electrode.

[0026] The all-solid-state lithium secondary battery may have an initial discharge capacity of 180 mAh / g or more.

[0027] (3) Beneficial effects

[0028] The composite positive electrode for an all-solid-state lithium secondary battery according to the present invention can improve the phenomenon of reduced ion conductivity of the sulfide-based solid electrolyte in the composite positive electrode.

[0029] The composite positive electrode according to the present invention may have excellent dispersibility of the positive electrode active material, the sulfide-based solid electrolyte, the positive electrode conductive material, and the binder, and may have high oxidation stability.

[0030] The initial discharge capacity of the all-solid-state lithium secondary battery including the composite cathode according to the present invention can be improved.

[0031] The composite cathode of the present invention can be widely used in electric vehicles, battery charging stations, and other green technology fields such as solar power generation and wind power generation using batteries. In addition, the composite cathode of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 These are images of the sheets of Examples 1-2 to 3-2 and Comparative Examples 1-2 to 3-2. Best Practice

[0033] Hereinafter, various embodiments according to the present invention will be described, but the implementation can be modified into various other forms, and the scope thereof is not limited to the embodiments described below.

[0034] Hereinafter, in this specification, unless otherwise specifically defined, when describing a layer, membrane, film, region, plate or the like as being "above" or "on" another part, this may include not only the case where it is "directly" "above" another part, but also the case where there are other parts in between.

[0035] In all-solid-state lithium secondary batteries, the electrodes disposed on both sides of the solid electrolyte layer can contact and combine with the solid electrolyte to form a composite electrode. However, in the case of a composite positive electrode, the positive electrode binder included in the composite positive electrode may reduce the ionic conductivity of the solid electrolyte, agglomerate between the composite positive electrode particles, and deteriorate oxidative stability.

[0036] The composite positive electrode for an all-solid-state lithium secondary battery according to a specific embodiment may include a sulfide-based solid electrolyte and may include a positive electrode binder, wherein the positive electrode binder is a positive electrode binder including a non-aromatic hydrocarbon-based butadiene rubber and a fluorine-based rubber. The composite positive electrode according to a specific embodiment of the present invention may have excellent ionic conductivity. In addition, the dispersibility of the positive active material of the composite positive electrode according to a specific embodiment of the present invention may be improved, and the oxidative stability may be improved.

[0037] Composite cathode

[0038] The composite positive electrode for an all-solid-state lithium secondary battery according to the present invention may include a positive electrode current collector and a positive electrode mixture layer formed on at least one side of the positive electrode current collector.

[0039] The positive electrode mixture layer may include a positive electrode active material, a positive electrode binder, and a solid electrolyte, and may further include a positive electrode conductive material.

[0040] The composite positive electrode according to one embodiment of the present invention may include a sulfide-based solid electrolyte and a positive electrode binder, and the positive electrode binder may include non-aromatic hydrocarbon-based butadiene rubber and fluorine-based rubber.

[0041] positive electrode active material

[0042] The positive electrode active material can also be applied to the present invention as long as it is a lithium transition metal oxide that can be generally used as a positive electrode active material in a secondary battery and can absorb and release lithium ions. For example, NCM-based lithium composite oxides, NCA-based lithium composite oxides or NCMA-based lithium composite oxides, LiMn 1.5 Ni 0.5Lithium composite oxides of manganese and nickel such as O4, lithium titanate, lithium cobaltate, lithium nickelate, lithium manganate, titanium oxide, niobium oxide, tungsten oxide, molybdenum oxide, LiMPO4 (M = Fe, Mn, Co, Ni), lithium metal phosphates such as Li3V2(PO4)3.

[0043] Specifically, the positive electrode active material can be Li a Ni x M 1-x O 2+y (where 0.9 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.99, -0.1 ≤ y ≤ 0.1, and M can represent one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba or Zr). Specifically, 0.95 ≤ a ≤ 1.08, x can be 0.6 or more, 0.8 or more, greater than 0.8, 0.9 or more, or 0.98 or more. In addition, specifically, M can include Co, Mn or Al, more specifically, M can include Co and Mn, and can further include Al as needed.

[0044] More specifically, the positive electrode active material can be composed of Li a (Ni x Co y Mn z )O2 (0.9 ≤ a ≤ 1.2, 0 < x ≤ 0.99, 0 < y < 0.5, 0 < z < 0.5, x + y + z = 1) represents an NCM-based positive electrode active material, or can also be an NCMA-based positive electrode active material further including Al therein, or can be composed of Li a (Ni x Co y Al <00,00014>)O2 (0.9 ≤ a ≤ 1.2, 0 < x < 0.99, 0 < y < 0.5, 0 < z < 0.5, x + y + z = 1) represents an NCA-based positive electrode active material. Among them, 0.95 ≤ a ≤ 1.08, x can be 0.6 or more, 0.8 or more, greater than 0.8, 0.9 or more, or 0.98 or more.

[0045] In addition, the positive electrode active material can be composed of Li 1+x M 1-xLLO (Lirich layered oxides, Over Lithiated Oxides, Over-lithiated layered oxide, OLO, LLOs) represented by O2, wherein 0≤x≤0.4, M may include at least one element of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba and Zr, specifically, M may include Ni, Co, Mn or Al, more specifically, M may include Ni, Co and Mn, and may further include Al as needed.

[0046] In some exemplary embodiments, the positive electrode active material may further include a dopant or coating on the surface. For example, the dopant or coating may include Al, Ti, Ba, Zr, Si, B, Mg, P, W, Na, V, Cu, Zn, Ge, Ag, Ba, Nb, Ga, Cr, Sr, Y, Mo, or alloys thereof or oxides thereof, which may be used alone or in combination of two or more. The above-mentioned dopant or coating can passivate the positive electrode active material, thereby further improving the puncture stability and life.

[0047] For example, the lithium transition metal oxide may be in the form of primary particles or secondary particles formed by aggregation of primary particles.

[0048] In addition, the lithium transition metal oxide may be a secondary particle in which a plurality of primary particles are assembled or aggregated to form a particle, or may be in a single particle form. The single particle form may represent a secondary particle in which, for example, a plurality of primary particles (for example, more than 10) are assembled or aggregated to form a particle. However, the single particle form does not exclude the situation in which single particles in the range of 2 to 10 are attached to or closely adhered to each other and have an overall form. In some embodiments, the positive active material may include both a secondary particle form and a single particle form.

[0049] When the lithium transition metal oxide comprises single-particle lithium transition metal oxide particles, cracks in the particles during battery charge and discharge are reduced, and the BET surface area that reacts with the electrolyte is reduced, thereby reducing side reactions between the electrolyte and the positive electrode active material. Therefore, the lifespan characteristics of the secondary battery and the capacity retention rate during repeated charge and discharge can be further improved.

[0050] In one embodiment, the positive electrode active material may be present in an amount of about 1 wt % to about 99 wt % based on the total weight of the positive electrode mixture layer.

[0051] Positive electrode conductive material

[0052] The positive electrode conductive material is used to impart conductivity to the electrode, and any positive electrode conductive material commonly used in secondary batteries may be used without limitation.

[0053] In an exemplary embodiment, the positive electrode conductive material can be a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, a metal-based material such as metal powder or metal fiber such as copper, nickel, aluminum, silver, a conductive polymer such as polyphenylene derivatives, or a conductive material including a mixture thereof.

[0054] In one embodiment, the positive electrode conductive material may be present in an amount of about 0.1 wt % to about 50 wt % based on the total weight of the positive electrode mixture layer.

[0055] solid electrolytes

[0056] The solid electrolyte may be a sulfide-based solid electrolyte.

[0057] In an exemplary embodiment, the sulfide-based solid electrolyte may include, for example, a sulfide-based solid electrolyte selected from the group consisting of Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2) and Li 7-x PS 6-x I x At least one of (0≤x≤2), but not particularly limited thereto.

[0058] In an exemplary embodiment, the sulfide-based solid electrolyte may be of an argyrodite type, and the argyrodite-type sulfide-based solid electrolyte may be represented by the following Chemical Formula 1.

[0059] [Chemical Formula 1]

[0060] Li + 12-n-x A n+ X 2- 6-x Y - x

[0061] In Chemical Formula 1, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, X is S, Se, or Te, Y is Cl, Br, I, F, CN, OCN, SCN, or N3, 1≤n≤5, and 0≤x≤2.

[0062] The sulfide-based solid electrolyte may be selected from, for example, Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6- x Br x (0≤x≤2) and Li 7-x PS 6-x I x (0≤x≤2) or more argyrodite-type sulfide-based solid electrolytes. In one embodiment, the sulfide-based solid electrolyte may be, for example, one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. The argyrodite-type sulfide-based solid electrolyte has excellent hardness, so that micronization of the solid electrolyte may not occur during the mixing process of forming the electrode, thereby suppressing additional side reactions with solvents and binders and ensuring the structural stability of the solid electrolyte.

[0063] In an exemplary embodiment, the particle size of the sulfide-based solid electrolyte may be about 10 μm or less. By having a particle size within the above range, excellent dispersibility may be achieved, thereby providing a composite positive electrode having a uniform surface.

[0064] In one embodiment, the sulfide-based solid electrolyte may be present in an amount of about 1 wt % to about 99 wt % based on the total weight of the positive electrode mixture layer.

[0065] positive electrode binder

[0066] As described above, in an exemplary embodiment, the positive electrode binder may include non-aromatic hydrocarbon-based butadiene rubber and fluorine-based rubber.

[0067] In one embodiment, the non-aromatic hydrocarbon-based butadiene rubber may include butadiene rubber (BR).

[0068] In one embodiment, the non-aromatic hydrocarbon-based butadiene rubber may have a weight average molecular weight of about 590,000 to about 720,000. In the present invention, the weight average molecular weight may be measured by a light scattering method.

[0069] In one embodiment, the fluorine-based rubber may include at least one of polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), and polyvinylidene fluoride-hexafluoropropylene (poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP).

[0070] In one embodiment, the fluorine-based rubber may have a weight average molecular weight of about 100,000 to about 600,000.

[0071] When the non-aromatic hydrocarbon-based butadiene rubber has a weight average molecular weight outside the above range or the fluorine-based rubber has a weight average molecular weight outside the above range, the viscosity of the slurry used to manufacture the positive electrode mixture layer may increase. As a result, it may be difficult to adjust the amount of slurry during coating the slurry onto the positive electrode current collector, making it difficult to manufacture a composite positive electrode with uniform thickness. In some cases, defects may occur in the positive electrode mixture layer during drying the slurry to form the positive electrode mixture layer.

[0072] In one embodiment, the positive electrode binder may include the non-aromatic hydrocarbon-based butadiene and the fluorine-based rubber in a weight ratio of about 1:99 to about 99:1.

[0073] In an exemplary embodiment, the positive electrode binder may further include at least one selected from polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropylmethyl cellulose (HPMC), polyvinylpyrrolidone (PTFE), polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), and styrene-butadiene rubber (SBR).

[0074] In one embodiment, the composite positive electrode may include the positive electrode conductive material and the positive electrode binder in a weight ratio of about 1:99 to about 99: 1. Specifically, the composite positive electrode may include the positive electrode binder and the positive electrode conductive material in a weight ratio of about 1:99 to about 20:80, and more specifically, the composite positive electrode may include the positive electrode binder and the positive electrode conductive material in a weight ratio of about 1:99 to about 10:90.

[0075] In one embodiment, the positive electrode binder may be present in an amount of about 0.1 wt % to about 10 wt % based on the total weight of the positive electrode mixture layer.

[0076] In addition, the sulfide-based solid electrolyte can have a high ionic conductivity close to that of a liquid electrolyte. When the sulfide-based solid electrolyte is not included in the composite positive electrode and exists independently, the sulfide-based solid electrolyte can have a high ionic conductivity. However, the sulfide-based solid electrolyte can be included in the composite positive electrode and mixed with the positive electrode binder. In this case, the ionic conductivity of the sulfide-based solid electrolyte may be reduced due to the non-conductive positive electrode binder. That is, due to the positive electrode binder, the sulfide-based solid electrolyte included in the composite positive electrode may have a reduced ionic conductivity compared to the sulfide-based solid electrolyte existing independently.

[0077] In addition, the positive electrode binder may cause the positive electrode active material, sulfide-based solid electrolyte and positive electrode conductive material in the composite positive electrode to agglomerate.

[0078] Furthermore, the cathode binder may have high chemical stability with the sulfide-based solid electrolyte and may have low oxidation stability within the composite cathode.

[0079] However, the composite positive electrode according to an embodiment of the present invention may include the positive electrode binder containing the non-aromatic hydrocarbon-based butadiene rubber and the fluorine-based rubber, and the positive electrode binder may have high chemical stability with the sulfide-based solid electrolyte. In addition, the positive electrode binder may improve the phenomenon of reduced ionic conductivity of the sulfide-based solid electrolyte in the composite positive electrode, may improve the dispersibility, and may have high oxidation stability.

[0080] Positive electrode current collector

[0081] The composition of the positive electrode current collector is not particularly limited, and a sheet (plate) or foil formed of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof may be used.

[0082] The all-solid-state lithium secondary battery according to the present invention may include the composite positive electrode and a solid electrolyte layer provided on at least one surface of the composite positive electrode.

[0083] Negative electrode

[0084] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer formed on at least one surface of the negative electrode current collector.

[0085] The composition of the negative electrode current collector is not particularly limited, and a sheet or foil formed of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof may be used.

[0086] The negative electrode mixture layer may include carbon-based active materials such as artificial graphite and natural graphite, silicon-based active materials such as silicon oxide (SiOx; 0 < x < 2), Si-C composites, and pure silicon (pure Si), and metals such as lithium metal as negative electrode active materials.

[0087] The negative electrode mixture layer may further include a negative electrode binder. Exemplarily, the negative electrode binder may include one or more of the following substances: styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc. [[ID=二十六]]

[0088] The negative electrode mixture layer may further include a negative electrode conductive material. For example, the negative electrode conductive material may include one or more of the following: graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes (CNTs); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0089] In addition, the all-solid-state lithium secondary battery may not include a negative electrode mixture layer (hereinafter also referred to as a non-negative electrode secondary battery). That is, it may be a battery in which a negative electrode mixture layer including a negative electrode active material is not formed on the negative electrode current collector during the assembly process of the battery. When the non-negative electrode lithium secondary battery is initially charged or charged for the first time, the main positive electrode active material and the sacrificial positive electrode active material are delithiated, and the lithium ions generated by the positive electrode active material are reduced on the negative electrode current collector, thereby forming a lithium metal layer or a solid lithium layer.

[0090] In one embodiment, the all-solid-state lithium secondary battery may include a lithium metal anode.

[0091] Solid electrolyte layer

[0092] The solid electrolyte layer may include at least one selected from the group consisting of a polymer solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, and a sulfide-based solid electrolyte.

[0093] In one embodiment, the solid electrolyte layer may include a sulfide-based solid electrolyte, wherein the sulfide-based solid electrolyte may be the sulfide-based solid electrolyte described above.

[0094] In one embodiment, when the solid electrolyte layer includes a sulfide-based solid electrolyte, the sulfide-based solid electrolyte may be the same as or different from the sulfide-based solid electrolyte of the composite cathode, for example, they may be the same as each other.

[0095] In one embodiment, the sulfide-based solid electrolyte of the solid electrolyte layer and the sulfide-based solid electrolyte of the composite positive electrode may be of argyrodite type.

[0096] As a specific embodiment of the present invention, by including the non-aromatic hydrocarbon-based butadiene rubber and the fluorine-based rubber as the positive electrode binder in the composite positive electrode, the phenomenon of reduced ionic conductivity of the sulfide-based solid electrolyte in the composite positive electrode can be improved, the dispersibility can be improved, and the oxidative stability can be high. Therefore, the initial discharge capacity of the all-solid-state lithium secondary battery can be improved.

[0097] In one embodiment, the all-solid-state lithium secondary battery may have an initial discharge capacity of about 180 mAh / g or more. DETAILED DESCRIPTION

[0098] The present invention will be described in more detail below with reference to the following examples. The following examples are provided to illustrate an example of the present invention and are not intended to limit the present invention.

[0099] Examples 1 to 3 and Comparative Examples 1 to 3

[0100] The composite positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 3 include NCM622 (Li (Ni 0.6 Co 0.2 Mn 0.2 )O2) as the positive electrode active material, including Timcal's carbon black Super P as the positive electrode conductive material, and including Li6PS5Cl as the solid electrolyte.

[0101] In addition, the composite positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 3 include positive electrode binders having the types and weight ratios shown in Table 1 below.

[0102] [Table 1]

[0103]

[0104] Evaluation of the reduction rate of ionic conductivity

[0105] Three zirconia balls with a diameter of 5 mm were placed in a 35 ml Thinky mixer container, and the sulfide-based solid electrolyte and the positive electrode binder were added to the Thinky mixer container together with the solvent in a weight ratio of 97:3. The mixture was then stirred at 2000 rpm for 3 minutes using the Thinky mixer to prepare a slurry.

[0106] The slurry was then coated on an Al foil to form a sheet, and then dried at 80° C. for 24 hours under a vacuum atmosphere to prepare a sulfide-based solid electrolyte-positive electrode binder sheet.

[0107] At this time, an ester-based organic solvent is used as the solvent.

[0108] Thus, sulfide-based solid electrolyte-positive electrode binder sheets of Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1, respectively including the positive electrode binders of Examples 1 to 3 and Comparative Examples 1 to 3, were prepared.

[0109] Afterwards, a dry sulfide-based solid electrolyte powder was prepared, and the ionic conductivities of the sulfide-based solid electrolyte powder and the sulfide-based solid electrolyte-positive electrode adhesive sheets of Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1 were measured.

[0110] Specifically, 0.1 g of the sulfide-based solid electrolyte powder was placed in a 10 mm mold, then pressurized at 350 MPa, and the ionic conductivity was measured. Subsequently, the sulfide-based solid electrolyte-positive electrode adhesive sheets of Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1 were cut into 10 mm pieces and placed in a 10 mm mold. The ionic conductivity was then measured for each of the sheets after pressurization at 350 MPa.

[0111] The ionic conductivity was measured using a potentiostat from Biologic. The measurement conditions for the ionic conductivity were set as follows: a start frequency of 7 MHz and an end frequency of 100 Hz with a value of 10 mV.

[0112] The ionic conductivity of the sulfide-based solid electrolyte powder and the sulfide-based solid electrolyte-positive electrode adhesive sheets of Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1 was measured three times to minimize the deviation. The ionic conductivity measurement was performed in a glove box in an argon (Ar) atmosphere.

[0113] Thereafter, the reduction rate of ionic conductivity of each sulfide-based solid electrolyte included in the sulfide-based solid electrolyte-positive electrode binder sheets of Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1 was calculated and evaluated according to Formula 1 below.

[0114] [Formula 1]

[0115]

[0116] Here, A is the measured value of the ionic conductivity of the sulfide-based solid electrolyte powder, and B is the measured value of the ionic conductivity of the sulfide-based solid electrolyte-positive electrode binder sheets of Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1.

[0117] When the reduction rate of ionic conductivity was less than 70%, it was evaluated as excellent, and when the reduction rate of ionic conductivity was 70% or more, it was evaluated as poor.

[0118] The evaluation results of the reduction rate of the ionic conductivity of the sulfide-based solid electrolyte are shown in Table 2 below.

[0119] [Table 2]

[0120]

[0121] Evaluation of dispersion

[0122] Three zirconia balls with a diameter of 5 mm were placed in a 35 ml Thinky mixer container, and the positive electrode conductive material and the positive electrode binder were added to the above Thinky mixer container together with the solvent in a weight ratio of 3:7. Then, the Thinky mixer was used to stir at a speed of 1500 rpm for 5 minutes to prepare a slurry.

[0123] At this time, Super P from Temeco was used as the positive electrode conductive material, an ester-based organic solvent was used as the solvent, and the positive electrode binders of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1 were used as the positive electrode binders.

[0124] Thereafter, the slurry was coated on an Al foil to form a sheet, and then dried under a vacuum atmosphere at a temperature of 120° C. for 24 hours, thereby preparing sheets of Examples 1-2 to 3-2 and Comparative Examples 1-2 to 3-2, respectively including the positive electrode binders of Examples 1 to 3 and Comparative Examples 1 to 3.

[0125] Thereafter, the extent to which the sheets of Examples 1-2 to 3-2 and Comparative Examples 1-2 to 3-2 were uniformly coated on the Al foil was visually observed, and the dispersibility of the sheets of Examples 1-2 to 3-2 and Comparative Examples 1-2 to 3-2 was evaluated as high / medium / low, respectively, based on the following criteria.

[0126] Top: The conductive material is not agglomerated and the slurry has good coating properties.

[0127] Middle: Some conductive material agglomeration was observed, but the slurry coating was good.

[0128] Bottom: The conductive material is more agglomerated and the slurry coating is also poor

[0129] The films of Examples 1-2 to 3-2 and Comparative Examples 1-2 to 3-2 were photographed and shown in FIG. Figure 1 The evaluation results of dispersibility are shown in Table 3 below.

[0130] [Table 3]

[0131]

[0132] Evaluation of oxidation stability

[0133] Three zirconia balls with a diameter of 5 mm were placed in a 35 ml Thinky mixer container, and the positive electrode conductive material and the positive electrode binder were added to the above Thinky mixer container together with the solvent in a weight ratio of 3:7. Then, the Thinky mixer was used to stir at a speed of 1500 rpm for 5 minutes to prepare a slurry.

[0134] At this time, Super P from Temeco was used as the positive electrode conductive material, an ester-based organic solvent was used as the solvent, and the positive electrode binders of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1 were used as the positive electrode binders.

[0135] Thereafter, the slurry was coated on an Al foil to prepare a composite positive electrode, and then the composite positive electrode was dried under a vacuum atmosphere at a temperature of 120° C. for 24 hours.

[0136] After that, a battery cell with lithium metal as the negative electrode is manufactured. The battery cell is in the form of a coin-shaped battery cell, composed of a composite positive electrode / separator / negative electrode, and uses a liquid electrolyte. At this time, polyethylene is used as the separator, and the liquid electrolyte used is a liquid electrolyte containing 1M LiPF6 electrolyte salt and 2% by weight of fluoroethylene carbonate (FEC) in an electrolyte solvent containing ethylene carbonate (EC) and ethyl methylcarbonate (EMC) in a weight ratio of 3:7.

[0137] Thus, battery cells of Examples 1-3 to 3-3 and Comparative Examples 1-3 to 3-3, respectively including the positive electrode binders of Examples 1 to 3 and Comparative Examples 1 to 3, were prepared.

[0138] Subsequently, the cells of Examples 1-3 to 3-3 and Comparative Examples 1-3 to 3-3 were evaluated for oxidation stability up to 5 V using a potentiostat from Biologic by linear sweep voltammetry (LSV). Cells with oxidation stability exceeding 4 V were evaluated as excellent, and cells with oxidation stability below 4 V were evaluated as poor. The evaluation results of the oxidation stability of the cells are shown in Table 4 below.

[0139] [Table 4]

[0140]

[0141] Measurement of initial discharge capacity

[0142] 21 zirconia balls with a diameter of 3 mm were placed in a 12 ml Thinky mixer container, and the positive electrode active material, sulfide-based solid electrolyte, positive electrode conductive material and positive electrode binder were mixed with a solvent in the above Thinky mixer container at a weight ratio of 80:17.5:1.5:1, and then stirred using a Thinky mixer, and then coated on an Al foil to prepare a sheet.

[0143] At this time, NCM622(Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) is used as the positive electrode active material, Li6PS5Cl is used as the sulfide-based solid electrolyte, Super P is used as the positive electrode conductive material, an ester-based organic solvent is used as the solvent, and the positive electrode adhesives of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1 above are respectively used as the positive electrode adhesive.

[0144] Thereafter, the sheet was dried under a vacuum atmosphere at a temperature of 80° C. for 24 hours, thereby manufacturing a composite positive electrode.

[0145] Then, an all-solid-state lithium secondary battery with a lithium-indium alloy as the negative electrode is manufactured. The all-solid-state lithium secondary battery consists of a composite positive electrode / solid electrolyte layer / negative electrode, wherein an argyrodite-type sulfide-based solid electrolyte is used as the solid electrolyte layer.

[0146] In detail, an argyrodite-type sulfide-based solid electrolyte was placed in a circular mold with a diameter of 10 mm and pressurized at 350 MPa to form the solid electrolyte layer, the composite positive electrode was arranged on one side of the solid electrolyte layer, and then pressurized at 300 MPa, and a negative electrode was arranged on the other side of the solid electrolyte layer, thereby preparing all-solid-state lithium secondary batteries of Examples 1-4 to Examples 3-4 and Comparative Examples 1-4 to Comparative Examples 3-4, respectively including the positive electrode binders of Examples 1 to Example 3 and Comparative Examples 1 to Comparative Examples 3, respectively.

[0147] Afterwards, the all-solid-state lithium secondary batteries of Examples 1-4 to 3-4 and Comparative Examples 1-4 to 3-4 were placed in pressure boxes, and their initial discharge capacities were measured.

[0148] In addition, the manufacturing process of the all-solid-state lithium secondary battery was carried out in a glove box under an argon (Ar) atmosphere, and the initial discharge capacity was measured at room temperature (25°C) at a C-rate of 0.05C and a cut-off voltage of 1.9V to 3.7V. The results of the initial discharge capacity of the all-solid-state lithium secondary battery are shown in Table 5 below.

[0149] [Table 5]

[0150]

[0151] See Tables 2 to 5 above and Figure 1 It can be confirmed that in the composite positive electrodes including the positive electrode binders of Examples 1 to 3 in Table 1, the chemical stability of the positive electrode binder with the sulfide-based solid electrolyte is excellent compared with the composite positive electrodes of Comparative Examples 1 to 3, and the reduction rate of the ionic conductivity of the sulfide-based solid electrolyte is low. At the same time, the dispersibility with the positive electrode conductive material, etc. is excellent, so it can be uniformly coated on the Al foil to form a composite positive electrode.

[0152] Furthermore, it was confirmed that the composite positive electrodes using the positive electrode binders of Examples 1 to 3 in Table 1 can produce all-solid-state lithium secondary batteries having excellent oxidation stability and high initial discharge capacity.

[0153] Thus, it can be confirmed that the composite positive electrode according to the present invention improves the phenomenon of reduced ionic conductivity of the sulfide-based solid electrolyte in the composite positive electrode by including the positive electrode binder containing the non-aromatic hydrocarbon-based butadiene rubber and the fluorine-based rubber. In addition, it can be seen that the dispersibility of the positive electrode active material, the sulfide-based solid electrolyte, and the positive electrode conductive material in the composite positive electrode of the present invention is improved, and the positive electrode binder has high oxidation stability. In addition, it can be seen that the initial discharge capacity of the all-solid-state lithium secondary battery including the composite positive electrode of the present invention is improved.

[0154] The embodiments of the present invention have been described in detail above, but these embodiments are merely exemplary, and those skilled in the art will appreciate that various modifications and equivalent embodiments may be obtained. Therefore, the true technical protection scope of the present invention should be determined by the technical concepts of the claims.

[0155] The specific implementation form described in the embodiment is one embodiment and does not limit the scope of the embodiment in any way. In addition, if "essential" or "important" is not specifically mentioned, it may not be a component that is essential for the application of the present invention.

[0156] The use of the term "said" and similar indicative terms in the description of the embodiments (especially in the claims) can correspond to both the singular and the plural. In addition, when a range is described in the embodiments, the disclosure of the application of individual values ​​falling within the above range is included (unless otherwise stated to the contrary), which is equivalent to describing each individual value constituting the above range in the detailed description.

[0157] Finally, if there is no clear description or contrary description of the order of the steps constituting the method according to the embodiment, the above steps can be performed in an appropriate order. The embodiment is not necessarily limited to the order of the description of the above steps. In the embodiment, the use of all examples or exemplary terms (e.g., etc.) is simply used to describe the embodiment in detail, and unless otherwise defined in the claims, the scope of the embodiment is not limited by the above examples or exemplary terms. In addition, it is known to those skilled in the art that various modifications, combinations and changes can be made according to design conditions and factors within the scope of the claims or their equivalents.

Claims

1. A composite positive electrode for an all-solid-state lithium secondary battery, comprising: sulfide-based solid electrolytes; and A positive electrode binder comprising non-aromatic hydrocarbon-based butadiene rubber and fluorine-based rubber.

2. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein The non-aromatic hydrocarbon-based butadiene rubber includes butadiene rubber (BR).

3. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein The fluorine-based rubber includes at least one of polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), and polyvinylidene fluoride-hexafluoropropylene (poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP).

4. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein The sulfide-based solid electrolyte is of argyrodite type.

5. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein The positive electrode binder includes the non-aromatic hydrocarbon-based butadiene and the fluorine-based rubber in a weight ratio of 1:99 to 99:

1.

6. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein: The non-aromatic hydrocarbon-based butadiene rubber has a weight average molecular weight of 590,000 to 720,000.

7. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein: The fluorine-based rubber has a weight average molecular weight of 100,000 to 600,000.

8. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein: The composite positive electrode for an all-solid-state lithium secondary battery further includes a positive electrode conductive material. The composite positive electrode for an all-solid-state lithium secondary battery includes the positive electrode conductive material and the positive electrode binder in a weight ratio of 1:99 to 99:

1.

9. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 1, wherein: The sulfide-based solid electrolyte is of argyrodite type, and the positive electrode binder includes butadiene rubber and fluorine-based rubber.

10. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 9, wherein: The fluorine-based rubber includes at least one of polyvinylidene fluoride, polyhexafluoropropylene, and polyvinylidene fluoride-hexafluoropropylene.

11. The composite positive electrode for an all-solid-state lithium secondary battery according to claim 9, wherein: The non-aromatic hydrocarbon-based butadiene rubber includes butadiene rubber.

12. An all-solid-state lithium secondary battery, comprising: A composite positive electrode comprising a sulfide-based solid electrolyte and a positive electrode binder, wherein the positive electrode binder comprises non-aromatic hydrocarbon-based butadiene rubber and fluorine-based rubber; as well as A solid electrolyte layer is provided on at least one side of the composite positive electrode.

13. The all-solid-state lithium secondary battery according to claim 12, wherein: The non-aromatic hydrocarbon-based butadiene rubber includes butadiene rubber.

14. The all-solid-state lithium secondary battery according to claim 12, wherein: The fluorine-based rubber includes at least one of polyvinylidene fluoride, polyhexafluoropropylene, and polyvinylidene fluoride-hexafluoropropylene.

15. The all-solid-state lithium secondary battery according to claim 12, wherein: The sulfide-based solid electrolyte is of argyrodite type.

16. The all-solid-state lithium secondary battery according to claim 12, wherein: The solid electrolyte layer includes a sulfide-based solid electrolyte.

17. The all-solid-state lithium secondary battery according to claim 12, wherein: The sulfide-based solid electrolyte of the solid electrolyte layer and the sulfide-based solid electrolyte of the composite positive electrode are of argyrodite type.

18. The all-solid-state lithium secondary battery according to claim 12, wherein: The all-solid-state lithium secondary battery further includes a lithium metal negative electrode.

19. The all-solid-state lithium secondary battery according to claim 12, wherein: The all-solid-state lithium secondary battery has an initial discharge capacity of more than 180 mAh / g.

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