Binder resin for sulfide-based all-solid-state secondary battery, and electrolyte layer, composite negative electrode layer, and secondary battery comprising same

Abstract

The present invention relates to a binder resin for a sulfide-based all-solid-state secondary battery, and an electrolyte layer, a composite negative electrode layer, and a secondary battery comprising same. More specifically, the binder resin according to the present invention can reinforce the bonding between an electrode current collector and an electrode active material, and can enhance adhesion through chemical and physical interactions with the electrode active material to mitigate the thermal expansion of an electrode and the deformation during the lifetime of the electrode, leading to an improvement in the stability of the electrode during charge-discharge cycles of the battery.

Description

Binder resin for sulfide-based all-solid-state secondary batteries, electrolyte layer containing the same, composite anode layer, and secondary battery

[0001] The present invention relates to a binder resin for a sulfide-based all-solid-state secondary battery, an electrolyte layer including the same, a composite negative electrode layer, and a secondary battery.

[0002]

[0003] Lithium secondary batteries boast higher energy densities than conventional batteries, making them a popular energy source for applications such as portable electronic devices and electric vehicles. However, the liquid electrolytes used in existing lithium secondary batteries, which have been in widespread use for a long time, primarily rely on highly flammable organic solvents, leading to persistent safety issues. Consequently, all-solid-state lithium secondary batteries utilizing solid electrolytes have attracted attention, offering the potential to overcome the stability issues previously associated with liquid electrolytes.

[0004] In particular, in the case of an all-solid-state secondary battery based on a sulfide-based solid electrolyte, Li having a high ionic conductivity of 25 mS / cm 10 GeP2S 12 Since the crystal structure of the (LGPS) series became known, research has been actively conducted to commercialize all-solid-state lithium secondary batteries based on sulfide-based solid electrolytes.

[0005] Sulfide-based solid electrolytes have the advantageous characteristics of higher ionic conductivity than oxide-based solid electrolytes and higher mechanical strength than polymer-based solid electrolytes in terms of lithium ion conduction, but sulfide-based solid electrolytes have the disadvantageous characteristic of reduced ionic conductivity due to their high chemical reactivity with moisture and oxygen, which leads to side reactions. Due to moisture and oxidation and side reaction problems, LPSCl, LPS, LGPS, more specifically LI2S-P2S5, Li2S-P2S5-LiX (X = halogen atoms), 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, n are positive numbers, Z is one of Ge, Zn or Ga), Li x M' y PS z A w In the case of sulfide-based solid electrolytes such as (x, y, z, w are all 0 or more and 6 or less, M' is one of Ge, Sn, or Si, A is one of F, Cl, Br, or I), there is a problem that they are vulnerable to polar solvents such as NMP and H2O applied to wet processes. To solve this stability problem, research is being conducted on manufacturing binders based on wet processes for secondary batteries using non-polar solvents such as hexane, heptane, toluene, xylene, xexylbutyrate isoamyl ether, butyl butyrate, benzyl acetate, and anisole.

[0006] Sulfide-based solid-state secondary batteries require a sheet-type solution process to form a thin and homogeneous solid electrolyte layer, which is directly related to the energy density of the battery, while being mass-produced through a roll-to-roll method. This has increased the importance of the binder, an essential element in the electrode manufacturing process. In particular, the importance of the binder is greater in the field of sulfide-based solid-state secondary batteries, where all electrode materials are in a solid state, than in lithium secondary batteries with liquid electrolytes. This problem begins with the problem of disconnection between electrode materials caused by volume changes in the active material that occur during the charge and discharge process of sulfide-based solid-state secondary batteries. This is because once the electrode material interface is disconnected due to weak adhesion between the active material and the binder, the electrode material cannot develop capacity within the electrode. Therefore, in sulfide-based solid-state secondary batteries, the binder has a meaning that goes beyond simply connecting the electrode materials.

[0007] Meanwhile, the adhesive properties of polymer binders are determined by the flexibility and structural characteristics of the polymer chains. Continuous polymer chains suppress volume expansion of the electrode material, contributing to improved electrode adhesion. Conventional polymer binders with this polymer structure, such as polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and carboxymethyl cellulose (CMC), exhibit high adhesive strength due to their strong polar functional groups. However, they are chemically soluble only in highly polar solvents (e.g., NMP and H2O), making them unsuitable as binders for sulfide-based all-solid-state lithium secondary batteries.

[0008] Korean Patent No. 10-1693636 discloses a binder resin composition for a sulfide-based solid electrolyte comprising a block copolymer including a polar group and a non-polar group such as polyethylene glycol-block-polypropylene glycol-block-polyethylene glycol (PEG-PPG-PEG) or polyethylene glycol-block-polypropylene glycol (PEG-PPG) and an organic solvent, and a sulfide-based solid electrolyte using the same, and Japanese Patent No. 6985516 discloses a solid electrolyte using polyurethane, polyimide, etc. as a particle-type binder, and an all-solid-state secondary battery including the same.

[0009] Currently reported solution-processed sulfide-based all-solid-state secondary batteries use binders that can be dispersed in nonpolar or very low-polarity polar aprotic solvents such as xylene and toluene, such as butadiene rubber (BR), styrene butadiene rubber (SBR), styrene ethylene butylene styrene copolymer (SEBS), nitrile-butadiene rubber (NBR), and ethyl cellulose. However, the adhesion of the electrodes is insufficient, and information on the bonding mechanism within the electrodes is also insufficient.

[0010]

[0011] The purpose of the present invention is to provide a binder resin for a sulfide-based all-solid-state secondary battery, which is chemically stable with a sulfide-based solid electrolyte and a non-polar solvent, and which provides high adhesion between a current collector, an electrode, and a sulfide-based solid electrolyte, thereby exhibiting excellent lifespan characteristics of the battery, and an electrolyte layer, a composite negative electrode layer, and a secondary battery comprising the same.

[0012] The objectives of the present invention are not limited to those mentioned above. Other objectives and advantages of the present invention not mentioned above can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the objectives and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0013]

[0014] To achieve the above object, one example of the present invention provides a binder resin for a sulfide-based all-solid-state secondary battery, which includes a hard segment including a urethane unit and a soft segment including a polyester unit.

[0015] In addition, another example of the present invention provides a composite negative electrode layer and electrolyte layer for a sulfide-based all-solid-state secondary battery including the binder resin.

[0016] In addition, another example of the present invention provides a sulfide-based all-solid-state secondary battery including the composite cathode layer or the electrolyte layer.

[0017] Furthermore, another example of the present invention provides a sulfide-based all-solid-state secondary battery including a composite negative electrode layer for a sulfide-based all-solid-state secondary battery including the binder resin; and an electrolyte layer for a sulfide-based all-solid-state secondary battery including the binder resin.

[0018]

[0019] The binder resin according to the present invention has excellent adhesive properties, and can strengthen the bond between the electrode current collector and the electrode active material, and can improve the adhesive strength through chemical and physical interactions with the electrode active material.

[0020] In addition, the binder resin according to the present invention is flexible and has excellent bonding strength, thereby alleviating thermal expansion of the electrode and deformation caused by it, thereby improving the stability of the electrode during the charge / discharge cycle of the battery.

[0021] In addition, the binder resin according to the present invention can lower the interfacial resistance of a sulfide-based all-solid-state and has high binding force, thereby improving the performance of a battery based on effective ion conductivity.

[0022]

[0023] Figure 1 is a graph showing the adhesive properties of a sulfide-based solid electrolyte layer according to Example 2 and Comparative Example 1.

[0024] Figure 2 is a graph showing the ionic conductivity characteristics of a sulfide-based solid electrolyte layer according to Example 2 and Comparative Example 1.

[0025] Figure 3 is a graph showing the adhesive properties of the composite cathode layer according to Example 3 and Comparative Example 2.

[0026] Figure 4 is a graph showing the charge and discharge characteristics of a sulfide-based all-solid-state secondary battery according to Example 4 and Comparative Example 3.

[0027] Figure 5 is a graph showing the life characteristics of a sulfide-based all-solid-state secondary battery according to Example 4 and Comparative Example 3.

[0028]

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0030]

[0031] Sulfide-based all-solid-state secondary battery binder resin

[0032] As a first embodiment of the present invention, a binder resin for a sulfide-based all-solid-state secondary battery is provided, which includes a hard segment including a urethane unit and a soft segment including a polyester unit.

[0033] To explain this in detail, it is as follows.

[0034] The above binder resin may include a hard segment and a soft segment.

[0035] The above hard segment may include a urethane unit.

[0036] The urethane unit of the hard segment may be derived from the -OH group of a polyol (e.g., a diol) and a chain extender (e.g., an aliphatic diol) and the isocyanate group (-NCO) of a diisocyanate. In addition, the hard segment may include at least one of an aromatic and an aliphatic urethane unit.

[0037] The above aromatic urethane unit may refer to a urethane unit that includes an aromatic ring structure within its structure. The aliphatic urethane unit may refer to a urethane unit that includes an aliphatic (e.g., alkyl) structure within its structure. For example, the aromatic and aliphatic urethane units may be derived from the -OH group of a polyol and the isocyanate group (-NCO) of an aromatic diisocyanate (e.g., methylene diphenyl diisocyanate; MDI and hexamethylene diisocyanate; HDI). In addition, as described above, they may also be derived from aromatic and aliphatic diisocyanates and chain extenders.

[0038] It is preferred that the above soft segment comprises a polyester unit.

[0039] The polyester unit of the above soft segment may be derived from polyester polyol.

[0040] The polyester polyol may include at least one selected from the group consisting of random polyester polyols produced by the addition reaction of a polyfunctional carboxylic acid compound and a polyfunctional alcohol compound. As a specific example, the molar ratio of the polyfunctional alcohol to the polyfunctional carboxylic acid is introduced into a batch reactor at 1:1.05 to 1.50, mixed, and then heated from room temperature to 150°C, maintained at the first heating temperature of 150°C for about 90 minutes, then heated again from 150°C to 220°C, and maintained at the second heating temperature of 220°C for about 30 minutes. After applying a vacuum of 720 mmHg at the second heating temperature, the reaction is terminated when the acid value becomes 1 mgKOH / g or less, thereby producing a polyester polyol having a hydroxyl value of 40 to 230 mgKOH / g. The above hydroxyl value can be measured, for example, according to ASTM D 4274.

[0041] The above binder resin does not react with a sulfide-based solid electrolyte, and has excellent solubility and adhesive properties in a non-polar solvent, so that it can reduce the adhesive force between solid electrolytes, the interfacial resistance between a current collector, a conductive material, and an active material, etc., and at the same time increase the strength, thereby improving the mechanical properties of a sulfide-based solid electrolyte including the binder composition when forming the final tensile strength.

[0042] The process for producing the above binder resin may include both a pre-polymer process and a one-shot process, either a batch process or a continuous process. As a specific example, the binder resin may be produced by reacting the above-described components together in a one-shot polymerization process, and the diisocyanate molar ratio for the polyester polyol or the mixture of the polyester polyol and the diol is 1.0 to 0.90 to 1.0, and the mixture is mixed in a pre-mixer and fed into a continuous reaction extruder heated to 180 to 240°C to react, and then the reactant in which the reaction is completed is extruded to produce a binder resin in the form of pellets.

[0043] The above binder resin preferably has a weight average molecular weight of 30,000 to 150,000 g / mol. If the weight average molecular weight of the thermoplastic polyurethane is less than 30,000 g / mol, the chain bonding force of the binder resin may not have sufficient adhesive strength as a binder, and if it exceeds 150,000 g / mol, the interaction ratio between the binder and the solvent is reduced, so that the solubility in a non-polar solvent is lowered, and thus the solubility of the binder in the solvent may be reduced.

[0044] The above binder resin preferably has a melting point (Tm) of 30°C to 80°C. The melting point (Tm) may be after the crystallization temperature in the case of a semi-crystalline polymer, and can be defined as the temperature at which the polymer's physical properties can have flowability when the polymer chains can move freely. More specifically, it is the temperature at which the crystalline portion, excluding the amorphous portion, of a crystalline polymer melts, and melting of the polymer means that the polymer chains lose their regular arrangement.

[0045] The above binder resin preferably has a glass transition temperature (Tg) of -60°C to 0°C. The glass transition temperature (Tg) refers to the starting point of the transition from a glassy state to a rubbery state, and from a chemical perspective, it can be defined as the temperature at which small segments of a polymer begin segmental motion. More specifically, the glassy state refers to an amorphous state that does not have a crystalline structure that a general solid has, but is a non-fluidic solid state, and the rubbery state refers to a state in which an object can exhibit a slight flow behavior, such as the behavior of an elastic body. In addition, the transition state refers to a change from the glassy state to the rubbery state that occurs within a temperature range.

[0046] The binder resin preferably has a polarity of 0.001 to 3.5. Specifically, the binder resin may be characterized by being soluble in an organic solvent having a polarity of 0.001 to 3.5, preferably 0.1 to 3.3. When the polarity is less than 0.001, there is a problem of reduced ionic conductivity, and when it exceeds 3.5, there is a problem of excessively high polarity, which may cause a side reaction with a sulfide-based solid electrolyte.

[0047] The binder resin according to the present invention having the conditions described above does not react with a sulfide-based solid electrolyte, and has excellent solubility and adhesive properties in a non-polar solvent, so that it can reduce the adhesive strength between all-solid-state electrolytes and the interfacial resistance between a current collector, a conductive material, and an active material, and at the same time increase the strength, thereby improving the mechanical properties of a sulfide-based solid electrolyte including the binder resin composition when forming the final tensile strength.

[0048] The above-described binder resin is preferably a urethane-based resin, specifically a thermoplastic polyurethane (TPU) containing aromatic and aliphatic urethane units and polyester units.

[0049] According to another embodiment of the present invention, a binder resin composition for a sulfide-based all-solid-state secondary battery can be provided, characterized in that it includes, as a binder resin, thermoplastic polyurethane; a non-polar solvent; and a sulfide-based solid electrolyte.

[0050] The above non-polar solvent includes at least one selected from the group consisting of toluene, xylene, hexane, heptane, dodecane, chlorobenzene, 1,2-dichlorobenzene, 1,2-dichloroethane, iso-butylbutylate, cyclohexane, benzene, anisole, chloroform, diethyl ether, tetrahydrofuran, and 1,6-dichlorohexane.

[0051] The above nonpolar solvent is a nonpolar organic solvent having a Polarity Index (P) of 0.001 to 3.5, and may be characterized by good dispersibility without causing a side reaction with the sulfide-based solid electrolyte. In this case, when the P value is less than 0.001, the binding force with polar functional groups existing on the surface of the current collector or active material of the sulfide-based solid electrolyte and the all-solid-state secondary battery including the same may decrease, resulting in insufficient adhesive strength as a binder. In addition, when the P value exceeds 3.5, a side reaction with the sulfide-based solid electrolyte may occur, resulting in a deterioration in performance.

[0052] The binder resin according to the present invention is compatible with a sulfide-based solid electrolyte and has an adhesive strength greater than that of a butadiene rubber (BR)-based binder.

[0053]

[0054] Electrolyte layer and composite cathode layer

[0055] As another embodiment of the present invention, an electrolyte layer and a composite negative electrode layer including the binder resin for a sulfide-based all-solid-state secondary battery described above are provided.

[0056] Detailed descriptions of overlapping parts with the above-described embodiment of the present invention have been omitted, but the contents described for one embodiment of the present invention can be equally applied even if the description is omitted in another embodiment.

[0057] Hereinafter, an electrolyte layer and a composite cathode layer according to another embodiment of the present invention will be described in detail.

[0058] In general, sulfide-based solid electrolytes are highly sensitive to moisture and oxygen, causing side reactions when polar solvents are used. Therefore, in order to ensure stability during the manufacture of sulfide-based solid electrolytes, they can be manufactured through a wet process using a nonpolar solvent. However, there is a problem in that commercial binders such as PVDF and SBR / CMC do not dissolve in nonpolar solvents, making them inapplicable to the wet process. In addition, when a nonpolar solvent is used in the binder resin composition for sulfide-based all-solid-state secondary batteries, the dispersion is not uniform when mixed into the sulfide-based solid electrolyte slurry, and after drying, the interfacial resistance between the active material and solid electrolyte and solid electrolyte-solid electrolyte increases during electrode formation, which can deteriorate ionic conductivity and battery performance. Accordingly, when manufacturing a binder composition for a sulfide-based solid electrolyte according to the present invention, a binder resin composition for a sulfide-based solid-state secondary battery containing a thermoplastic polyurethane including a hard segment and a soft segment and a lithium salt is used due to the need for a binder that can increase the adhesive strength between materials such as a current collector, a conductive material, and an active material forming an all-solid-state secondary battery and a solid electrolyte, thereby reducing the interfacial resistance.

[0059] That is, the electrolyte layer according to the present invention can be manufactured through a wet process using a non-polar solvent by including the above-described binder resin. Specifically, the electrolyte layer including the binder resin according to the present invention is uniformly dispersed in the process of mixing in a sulfide-based solid electrolyte slurry even when a non-polar solvent is applied, and after drying, when forming an electrode, the interfacial resistance between the active material-all-solid electrolyte and the all-solid electrolyte-all-solid electrolyte is not increased, thereby maintaining excellent ionic conductivity and battery performance. In addition, the binder resin according to the present invention can increase the adhesive strength between materials such as a current collector, a conductive material, and an active material constituting an all-solid-state secondary battery and the all-solid-state electrolyte layer, thereby reducing the interfacial resistance.

[0060] In another embodiment of the present invention, the electrolyte layer, specifically the sulfide-based solid electrolyte layer, can be manufactured by manufacturing the sulfide-based solid electrolyte layer using a slurry in which a nonpolar solvent and the binder resin composition are mixed, and coating and forming the manufactured composite cathode layer.

[0061] In another embodiment of the present invention, the sulfide-based solid electrolyte layer is argyrodites Li6PS5X (X=Cl, Br, I). Argyrodites have improved ionic conductivity and chemical stability by replacing some of the sulfur with halogen atoms. More preferably, Li6PS5Cl (LPSCl) can be used. LPSCl has high ionic conductivity (1.3×10 at room temperature). 3 S cm 1 ), which is more advantageous due to its low price and ease of manufacturing.

[0062] The sulfide-based solid electrolyte layer including the above binder composition may include the above-described binder resin in an amount of 0.1 to 20 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 5 parts by weight, based on 100 parts by weight of the sulfide-based solid electrolyte layer.

[0063] In another embodiment of the present invention, the composite anode layer can be manufactured through a thin film forming process such as coating an electrode slurry containing a sulfide-based all-solid electrolyte, a solvent, a binder resin, an active material, and conductive carbon on a copper current collector and then drying the electrode slurry. Here, the active material of the composite anode layer is artificial graphite, natural graphite, LTO (lithium titanium oxide, Li4Ti5O2). 12 ), one type can be selected from the group of silicon. Conductive carbon can be selected from the group of Super P, Denka Black, Carbon Nanotube (CNT), Carbon Nanofiber (CNF), Ketjenblack, Acetylene Black, and Graphene. This can be manufactured through thin film processing such as coating it on a copper current collector and then drying it.

[0064] The composite cathode layer including the above binder composition may include 0.1 to 20 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 5 parts by weight of the above-described binder resin based on 100 parts by weight of the electrode slurry.

[0065]

[0066] Sulfide-based all-solid-state secondary battery

[0067] As another embodiment of the present invention, a sulfide-based solid-state secondary battery is provided, which includes a sulfide-based solid electrolyte layer or composite negative electrode layer comprising a binder resin for a sulfide-based solid-state secondary battery manufactured according to the above manufacturing method.

[0068] Furthermore, another example of the present invention provides a sulfide-based all-solid-state secondary battery including a composite negative electrode layer for a sulfide-based all-solid-state secondary battery including the binder resin; and an electrolyte layer for a sulfide-based all-solid-state secondary battery including the binder resin.

[0069]

[0070] Hereinafter, a sulfide-based all-solid-state secondary battery according to the present invention will be described in detail.

[0071] An all-solid-state battery refers to a battery that uses a solid electrolyte instead of a separator and an electrolyte among the four major components of a conventional lithium-ion battery, which are a cathode, anode, a separator, and an electrolyte. The conventional liquid-type electrolyte has the disadvantages of causing the battery to expand when the liquid vaporizes into a gas at high temperatures and the vapor pressure increases, and of lowering the electrochemical performance due to a decrease in the chemical reaction rate at low temperatures. In place of this, the all-solid-state battery is more stable against external shocks and can prevent the battery from expanding by using a solid electrolyte. Typically, an all-solid-state battery is composed of a structure including a cathode, an anode, and a solid electrolyte layer in the form of a separator between the cathode and the anode. The present invention provides a sulfide-based all-solid-state secondary battery, which includes a cathode including a cathode active material, an anode including an anode active material, and a solid electrolyte layer formed between the cathode and the anode, wherein at least one of the cathode and the solid electrolyte layer includes a binder resin composition for a sulfide-based all-solid-state secondary battery according to the present invention.

[0072] The composite negative electrode layer or electrolyte layer included in the secondary battery may have the characteristics described above. For example, the sulfide-based all-solid-state secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a solid electrolyte layer formed between the positive electrode and the negative electrode, and at least one selected from the group consisting of the negative electrode and the electrolyte layer may include a binder resin as described above.

[0073] The above positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-xLithium manganese oxide (LiMnO2) such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Lithium nickel oxide, represented by O2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B or Ga and x is 0.01 to 0.3); chemical formula LiMn 2-x M x It may include a lithium manganese composite oxide represented by O2 (wherein M is Co, Ni, Fe, Cr, Zn or Ta, and x is 0.01 to 0.1) or Li2Mn3MO8 (wherein M is Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a portion of the lithium in the chemical formula is replaced by an alkaline earth metal ion; a disulfide compound; a composite oxide formed by Fe2(MoO4)3 or a combination thereof.

[0074] In addition, the above cathode active material is a high-nickel cathode active material, for example, Li[Ni 1-x-y-z Co x Mn y Al z O2 (wherein, x is 0.5 to 2, y is 0.5 to 2, and z is 0 to 2). Specifically, the positive electrode active material may be an NCM-based metal oxide in terms of improving material capacity and battery energy density.

[0075] The sulfide-based all-solid-state secondary battery according to the present invention may further include a conductive material. The conductive material may be a carbon-based conductive material. For example, the carbon-based conductive material may be at least one selected from the group consisting of carbon black, carbon fiber, carbon nanotubes, and graphite. Meanwhile, the carbon black may be at least one selected from the group consisting of acetylene black, Ketjen black, Super P, channel black, furnace black, lamp black, and thermal black. In addition, the graphite may be at least one selected from the group consisting of natural graphite and artificial graphite.

[0076]

[0077] Hereinafter, embodiments of the present invention will be described in detail so that those skilled 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 embodiments described herein.

[0078]

[0079] Example 1: Preparation of a binder resin for a sulfide-based all-solid-state secondary battery.

[0080] 52 wt% adipic acid and 48 wt% hexane diol were mixed, heated to 150°C, and reacted for 90 minutes, then heated again to 220°C and reacted for 30 minutes. A pressure of 720 mmHg was applied to the mixture after the reaction, and the reaction was terminated when the acid value became 1 mg KOH / g or less, thereby producing a polyester polyol having a hydroxyl value of 70 mg KOH / g. The polyester polyol thus produced was used as a soft segment, and toluene diisocyanate (TDI) was used as a hard segment, thereby producing a thermoplastic polyurethane having a hard segment content of about 10%.

[0081]

[0082] Example 2: Preparation of a sulfide-based all-solid-state electrolyte layer

[0083] An electrolyte mixture slurry was prepared by adding 97 wt% Li6PS5Cl as an all-solid electrolyte and 3 wt% of the polyurethane resin of Example 1 as a binder to 1,6-dichlorohexane as a dispersion medium. The electrolyte mixture slurry was applied to a stainless steel (SUS) thin film and dried to prepare a sulfide-based all-solid electrolyte layer.

[0084]

[0085] Example 3: Preparation of a composite cathode layer for a sulfide-based all-solid-state secondary battery

[0086] A negative electrode mixture slurry was prepared by adding 70 wt% of silicon-carbon mixed powder as a negative active material, 26 wt% of Li6PS5Cl as an all-solid electrolyte, 1.5 wt% of vapor grown carbon fibers (VGCF) as a conductive material, and 2.5 wt% of the polyurethane resin of Example 1 as a binder to 1,6-dichlorohexane as a dispersion medium. The negative electrode mixture slurry was applied to a stainless steel (SUS) thin film and dried to prepare a composite negative electrode layer.

[0087]

[0088] Example 4: Preparation of a sulfide-based all-solid-state secondary battery

[0089] The negative electrode of the above Example 3 was used as a working electrode, lithium metal was used as a counter electrode, and 150 mg of sulfide-based solid electrolyte powder Li6PS5Cl, which was cold-pressed at 150 MPa between these electrodes, was compressed by applying a pressure of 3.8 tons for 2 minutes, thereby manufacturing a sulfide-based all-solid-state secondary battery composed of a working electrode, an electrolyte layer, and a counter electrode.

[0090]

[0091] Comparative Example 1: Preparation of an electrolyte layer using a BR-based binder

[0092] A sulfide-based all-solid-state electrolyte layer was prepared in the same manner as in Example 2, except that 3 wt% of butadiene rubber (trade name: Sigma Aldrich, trade name: CAS RN: 9003-17-2 | Polybutadiene), which is used as a binder for existing sulfide solid electrolyte layers, was dissolved in 1,6-dichlorohexane (trade name: TCI chemicals, trade name: CAS RN: 2163-00-0 | 1,6-Dichlorohexane) as a dispersion medium.

[0093]

[0094] Comparative Example 2: Fabrication of a composite cathode layer using a BR-based binder

[0095] A composite cathode layer was manufactured in the same manner as in Example 3, except that 2.5 wt% of butadiene rubber (trade name: Sigma Aldrich, trade name: CAS RN: 9003-17-2 | Polybutadiene), which is used as a binder in existing composite cathode layers, was dissolved in 1,6-dichlorohexane (trade name: TCI chemicals, trade name: CAS RN: 2163-00-0 | 1,6-Dichlorohexane) as a dispersion medium.

[0096]

[0097] Comparative Example 3: Manufacturing of a sulfide-based all-solid-state secondary battery

[0098] A battery was manufactured by using the composite cathode layer of Comparative Example 2 as a working electrode, lithium metal as a counter electrode, and layering 150 mg of a sulfide-based solid electrolyte Li6PS5Cl cold-pressed at 150 MPa between these electrodes.

[0099]

[0100] Experimental Example 1: Analysis of the physical properties of binder resin

[0101] These measurements were performed using a differential scanning calorimeter (DSC Q20) connected to Differential Scanning Calorimeters (DSC) from TA instruments. Specifically, 10 mg of the cut sample of the binder resin prepared according to Example 1 was placed in an aluminum pan, covered with a lid, and crimped to prepare the sample. After setting the sample and reference sample at predetermined positions inside the cell, the measurement was performed under a nitrogen stream at a flow rate of 50 mL / min. The temperature was decreased from room temperature to -80°C at an increasing rate (scan rate) of 10°C / min, held for 1 minute, then increased to 150°C, decreased to -80°C, held at -80°C for 1 minute, and then increased to 150°C. The exothermic and endothermic peak temperatures derived from the crystallization of the recorded sample at this time were measured, and the Tg and Tm values ​​were calculated from the measured values.

[0102] As a result, the binder resin manufactured in Example 1 exhibited a Tg of -48°C and a Tm of 37°C.

[0103]

[0104] Experimental Example 2: Analysis of the adhesive properties of the electrolyte layer

[0105] The electrolyte layers of Example 2 and Comparative Example 1, manufactured in a size of 25×30 ㎟, were subjected to a 180° peel test at a speed of 12.5 mm / min using a universal testing machine (UTM).

[0106]

[0107] Experimental Example 3: Analysis of the ionic conductivity of the electrolyte layer

[0108] After laminating stainless steel thin film ion-blocking electrodes on both ends of a sulfide-based all-solid-state electrolyte, an AC voltage of 10 mV was measured through the electrodes on both sides of the sample using an electrochemical analyzer at 25°C. The frequency range was set to 0.1 Hz to 1 MHz, and the ionic conductivity of the bulk electrolyte was calculated from the intersection of the measured impedance trace with the real axis.

[0109]

[0110] Experimental Example 4: Analysis of Adhesive Properties of Composite Cathode Layers

[0111] The composite cathode layers of Example 3 and Comparative Example 2, manufactured in a size of 25×30 ㎟, were subjected to a 180° peel test at a speed of 12.5 mm / min using a universal testing machine (UTM).

[0112]

[0113] Experimental Example 5: Charge and Discharge Graphs of a Sulfide-Based All-Solid-State Secondary Battery

[0114] The sulfide-based all-solid-state secondary batteries of Example 4 and Comparative Example 3 were charged to 0.1 V at 0.1 C, and then fully charged while maintaining the voltage at a current of 0.05 C. Discharging was performed on each battery to 1.5 V at 0.1 C.

[0115]

[0116] Experimental Example 6: Lifetime characteristics of a sulfide-based all-solid-state secondary battery

[0117] The sulfide-based all-solid-state secondary batteries of Example 4 and Comparative Example 3 were charged to 0.1 V at 0.5 C, and then fully charged while maintaining the voltage at a current of 0.05 C. Each battery was discharged to 1.5 V at 0.1 C. This charge / discharge process was considered one cycle, and the life characteristics were observed for a total of 100 cycles.

[0118]

[0119] Figure 1 is a graph showing the adhesive properties of sulfide-based all-solid-state electrolyte layers according to Example 2 and Comparative Example 1. It was found that Example 2 had high structural stability of the electrolyte layer due to the high bonding strength of the polyurethane resin, but Comparative Example 1 had a problem in maintaining a stable structure of the electrolyte layer due to the relatively low bonding strength of the binder.

[0120] FIG. 2 is a graph showing the ionic conductivity characteristics of the sulfide-based solid-state electrolyte layer according to Example 2 and Comparative Example 1. The solid-state electrolyte layer of Example 2 has higher ionic conductivity than the solid-state electrolyte layer of Comparative Example 1, so that when a battery containing the electrolyte layer to which the binder of Example 2 is applied is driven, higher performance can be realized.

[0121] FIG. 3 is a graph showing the adhesive properties of composite cathode layers according to Example 3 and Comparative Example 2. It was found that Example 3 had stable bonding between electrode compositions due to the high bonding strength of the polyurethane resin, but Comparative Example 2 had a problem in that the adhesion between electrode compositions was relatively low due to the relatively low bonding strength of the binder.

[0122] FIG. 4 is a graph showing the charge and discharge characteristics of the sulfide-based all-solid-state secondary batteries according to Example 4 and Comparative Example 3. The secondary battery of Example 4 has a small internal electrode resistance and thus can obtain a larger initial capacity, but the secondary battery of Comparative Example 3 has a relatively large internal resistance, and it can be seen that the initial capacity development due to the proportional overvoltage is reduced.

[0123] FIG. 5 is a graph showing the life characteristics of sulfide-based all-solid-state secondary batteries according to Example 4 and Comparative Example 3. It was found that the secondary battery of Example 4 exhibited stable life characteristics due to alleviated electrode deformation caused by the high bonding strength of the polyurethane resin, but the secondary battery of Comparative Example 3 had problems in maintaining a stable life due to the relatively low bonding strength of the binder.

Claims

1. A binder resin for a sulfide-based all-solid-state secondary battery comprising a hard segment containing a urethane unit and a soft segment containing a polyester unit.

2. A binder resin for a sulfide-based all-solid-state secondary battery, characterized in that in claim 1, the urethane unit includes at least one of an aromatic urethane unit and an aliphatic urethane unit.

3. A binder resin for a sulfide-based all-solid-state secondary battery, characterized in that in the first paragraph, the polyester unit is derived from polyester polyol.

4. A binder resin for a sulfide-based all-solid-state secondary battery, characterized in that in the first paragraph, the binder resin has a weight average molecular weight of 30,000 to 150,000 g / mol.

5. A binder resin for a sulfide-based all-solid-state secondary battery, characterized in that in the first paragraph, the binder resin has a glass transition temperature (Tg) of -60 ℃ to 0 ℃.

6. A binder resin for a sulfide-based all-solid-state secondary battery, characterized in that in the first paragraph, the binder resin has a melting point (Tm) of 30°C to 80°C.

7. A binder resin for a sulfide-based all-solid-state secondary battery, characterized in that in the first paragraph, the binder resin has a polarity of 0.001 to 3.

5.

8. A sulfide-based all-solid-state secondary battery comprising a negative electrode layer for a sulfide-based all-solid-state secondary battery comprising a binder resin according to any one of claims 1 to 7.

9. A sulfide-based all-solid-state secondary battery comprising a sulfide-based all-solid-state electrolyte layer comprising a secondary battery binder resin according to any one of claims 1 to 7.

10. A composite negative electrode layer for a sulfide-based all-solid-state secondary battery comprising a binder resin according to any one of claims 1 to 7; and A sulfide-based all-solid-state secondary battery comprising an electrolyte layer for a sulfide-based all-solid-state secondary battery comprising a binder resin according to any one of claims 1 to 7.

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