Slurry composition for all-solid-state secondary battery and all-solid-state battery including the same

Abstract

The slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention includes a binder and an organic electrolyte, and the binder includes a polyimide-based compound.

Description

[Technical Field]

[0001] The present invention relates to a slurry composition for an all-solid-state secondary battery and an all-solid-state battery including the same. [Background technology]

[0002] Lithium-ion batteries have a much higher energy density per unit volume than other battery systems, and are currently widely used in electronic devices, etc., and are expanding their range of applications beyond small batteries to automobiles and energy storage devices.

[0003] However, since commonly known lithium ion batteries basically use a liquid electrolyte, safety issues related to explosion or fire have been occurring continuously.

[0004] As an alternative to such liquid electrolytes, solid electrolytes have been proposed, which can be broadly classified into three types: sulfide-based, polymer-based, and oxide-based. However, sulfide-based solid electrolytes are difficult to handle because they are highly reactive with the atmosphere and / or oxide-based positive electrode active materials such as LiCoO2, while polymer-based solid electrolytes have the disadvantage of being poor in thermal stability and deteriorating at high temperatures. Oxide-based solid electrolytes have a drawback of being difficult to handle because they are highly reactive with the atmosphere and / or oxide-based positive electrode active materials such as LiCoO2. -6 S / cm~10 -5 The problem is that it exhibits a relatively low ionic conductivity of 25 S / cm.

[0005] Therefore, for the commercialization of medium- to large-sized lithium-ion batteries, it is necessary to resolve the safety issues of liquid electrolytes and overcome the generally known drawbacks of solid electrolytes, such as high reactivity or low ionic conductivity, but research into this issue is still lacking. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a slurry composition for an all-solid-state secondary battery that has significantly improved ionic conductivity and electrochemical stability while eliminating the safety issues of liquid electrolytes by applying a specific binder that has increased flame retardancy and adhesive strength to an all-solid-state electrolyte composition from which inorganic substances have been removed. [Means for solving the problem]

[0007] A slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention includes a binder and an organic electrolyte, and the binder includes a polyimide-based compound.

[0008] The polyimide-based compound may be a fluorinated polyimide (FPI).

[0009] The organic electrolyte may be at least one selected from linear or cyclic carbonates, esters, ethers, polystyrene, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyacrylonitrile, and polysiloxane.

[0010] The slurry composition for an all-solid-state secondary battery may not contain an inorganic electrolyte.

[0011] The slurry composition for an all-solid-state secondary battery may further include at least one selected from a first organic compound, a lithium salt, and an additive.

[0012] The fluorinated polyimide (FPI) may be included in an amount of 1 wt % to 20 wt % of the total slurry composition for the all-solid-state secondary battery.

[0013] The binder may not include a polyvinylidene fluoride (PVdF) series binder.

[0014] The slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention may further include at least one selected from an electrode active material and a conductive material.

[0015] The slurry composition for an all-solid-state secondary battery according to the embodiment of the present invention has an ionic conductivity of 2.0×10 -2 It can be S / CM or more.

[0016] An all-solid-state secondary battery according to an embodiment of the present invention includes the slurry composition for an all-solid-state secondary battery. [Effects of the Invention]

[0017] By applying the slurry composition for an all-solid-state secondary battery of the present invention to an all-solid-state battery, the ionic conductivity and electrochemical stability can be significantly improved while eliminating the safety issues of liquid electrolytes. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing the results of measuring the ionic conductivity of solid electrolytes according to examples of the present invention and comparative examples. [Figure 2] FIG. 1 is a diagram showing the evaluation results of the battery chemical stability of solid electrolytes according to examples of the present invention and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] The advantages and features of the present invention, and the manner in which they are achieved, will become apparent from the following detailed description of the embodiments, but the present invention is not limited to the embodiments described herein and may be embodied in other forms.

[0020] As used herein, terms such as "comprises" should be understood as open-ended terms that encompass the possibility of including other embodiments.

[0021] As used herein, the terms "preferred" and "preferably" refer to embodiments of the invention that may offer certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or different circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

[0022] A slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention includes a binder and an organic electrolyte, and the binder includes a polyimide-based compound.

[0023] In the present invention, the term "totally solid" refers to a state that is neither gaseous nor liquid, and may include any general solid state or gel state.

[0024] The present invention has demonstrated that the electrochemical stability and ionic conductivity of a slurry composition for an all-solid-state secondary battery are improved by including an organic electrolyte and a polyimide-based compound.

[0025] As a more preferred example, the binder may be included in an amount of 8 wt % to 16 wt % of the entire slurry composition for an all-solid-state secondary battery.

[0026] As a more preferred example, the polyimide-based compound may be a fluorinated polyimide (FPI).

[0027] The present invention has demonstrated the effect of improving electrochemical stability and ionic conductivity by using both an organic electrolyte and a fluorinated polyimide (FPI) binder.

[0028] In a more preferred example, the binder may not include a polyvinylidene fluoride (PVdF)-based binder. For example, the binder may not include poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP).

[0029] Polyvinylidene fluoride (PVdF)-based binders are widely used as conventional binders. In the present invention, fluorinated polyimide (FPI) is applied to an all-solid-state secondary battery together with an organic electrolyte instead of the polyvinylidene fluoride-based binder, thereby achieving significantly improved electrochemical stability and ionic conductivity.

[0030] In addition, the use of fluorinated polyimide (FPI) has higher thermal stability than polyvinylidene fluoride (PVdF), resulting in improved flame retardancy. It also suppresses electrode crack formation. Furthermore, it improves battery life through uniform SEI formation and suppression of metal elution.

[0031] As a more preferred example, the fluorinated polyimide (FPI) may be included in an amount of 1 wt % to 20 wt %, or 5 wt % to 10 wt %, based on the total weight of the slurry composition for the all-solid-state secondary battery.

[0032] As a more preferred example, the fluorinated polyimide may be contained in an amount of 50% by weight to 80% by weight, or 60% by weight to 70% by weight, based on the total weight of the binder.

[0033] As a more preferred example, the binder may further include hydroxypropyl cellulose.

[0034] As a more preferred example, the hydroxypropyl cellulose may be contained in an amount of 20% by weight to 50% by weight, or 30% by weight to 40% by weight, based on the total weight of the binder.

[0035] A slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention includes an organic electrolyte.

[0036] For example, the organic electrolyte may be at least one selected from linear or cyclic carbonates, esters, and ethers prepared using an organic solvent.

[0037] For example, the carbonate may be one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

[0038] For example, the ester may be any one or more selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0039] For example, the ether may be any one or more selected from dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0040] More preferably, the solvent may include a mixed solvent of ethylene carbonate, which has a high dielectric constant, and propylene carbonate, which has a relatively lower melting point than ethylene carbonate.

[0041] The organic electrolyte may include at least one polymer selected from polystyrene, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyacrylonitrile, and polysiloxane.

[0042] As a more preferred example, the organic electrolyte may be contained in an amount of 40% by weight to 65% by weight, or 50% by weight to 60% by weight, based on the total weight of the slurry composition for an all-solid-state secondary battery.

[0043] In a more preferred example, the slurry composition for an all-solid-state secondary battery may not contain an inorganic electrolyte.

[0044] Among various types of solid electrolytes, currently, composite solid electrolytes containing active inorganic fillers in a polymer matrix are known to be the most advantageous for achieving excellent ionic conductivity and excellent interfacial contact with electrodes.

[0045] However, the present invention has eliminated the inorganic material from the organic-inorganic composite solid electrolyte and applied a polyvinylidene fluoride binder together, thereby solving the problems of the difference in ionic conductivity between organic and inorganic materials and the interface resistance, and has achieved the effect of significantly improving ionic conductivity by ensuring smooth ion mobility.

[0046] By eliminating inorganic substances, the present invention can eliminate the disadvantages of existing sulfide-based solid electrolytes, such as their high reactivity with air and / or oxide-based positive electrode active materials, making them difficult to handle, and the disadvantages of existing oxide-based solid electrolytes, such as their low ionic conductivity. At the same time, the present invention can improve electrochemical stability by using a polyvinylidene fluoride-based binder.

[0047] For example, the slurry composition for an all-solid-state secondary battery of the present invention may not contain an oxide-based, phosphate-based, nitride-based, or sulfide-based inorganic electrolyte.

[0048] As an example of the inorganic electrolyte not included, the oxide-based electrolyte may be lithium lanthanum zirconium oxide (LLZO) or lithium lanthanum titanium oxide (LLTO), the phosphate-based electrolyte may be lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP) or lithium silicon titanium phosphate (LSTP), the nitride-based electrolyte may be lithium phosphorus oxynitride (LiPON), and the sulfide-based electrolyte may be thio-LISICON.

[0049] The slurry composition for an all-solid-state secondary battery may further include at least one selected from a first organic compound, a lithium salt, and an additive.

[0050] Examples of the first organic compound that can be prepared by being contained in the slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention include linear aliphatic hydrocarbons such as hexane; cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone, diisobutyl ketone, and cyclohexanone; esters such as ethyl acetate, butyl acetate, butyl butyrate, γ-butyrolactone, and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran, ethylene glycol diethyl ether, and n-butyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; and amides such as N-methylpyrrolidone and N,N-dimethylformamide.

[0051] In a more preferred example, the first organic compound may include N-methyl-2-pyrrolidone (NMP). The present invention can improve the performance of an all-solid-state battery by applying an inorganic-free electrolyte and N-methyl-2-pyrrolidone (NMP) together with a polyimide binder, particularly a fluorinated polyimide (FPI).

[0052] In a more preferred example, the first organic compound may further include a ketone, in which case the ketone may be acetone.

[0053] As a more preferred example, the first organic compound may be included in an amount of 20% by weight to 50% by weight, or 30% by weight to 40% by weight, based on the total weight of the slurry composition for an all-solid-state secondary battery.

[0054] Lithium salts that can be prepared by being contained in the slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiAlO4, LiCH3SO3, LiFSI (lithium fluorosulfonyl imide, LiN(SO2F)2), LiTFSI (lithium(bis)trifluoromethanesulfonimide, LiN(SO2CF3)2), and LiBETI (lithium bisperfluoroethanesulfonimide, LiN(SO2C2F5)2), LiPF6, LiBF4, LiCH3CO2, LiCF3CO2, LiCH3SO3, LiFSI, LiTFSI, and LiN(C2F5SO2)2. In a more preferred example, when LiPF6 and / or LiFSi is used, the performance of the all-solid-state battery of the present invention can be improved.

[0055] The additive that may be included in the slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention may be at least one selected from fluoroethylene carbonate (FEC), vinylidene carbonate (VC), propanesultone (PS), propanesultone (PRS), and phosphazene compounds, but is not limited thereto.

[0056] When the slurry composition for an all-solid-state secondary battery according to the embodiment of the present invention is used to form a solid electrolyte layer, it may not contain an electrode active material and a conductive material.

[0057] However, when the slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention is used in an electrode mixture layer, it may further contain an electrode active material and / or a conductive material.

[0058] For example, the positive electrode active material may be a lithium-containing transition metal oxide, which is a compound capable of reversible intercalation and deintercalation of lithium, but is not limited thereto.

[0059] For example, the negative electrode active material may be any material capable of reversibly intercalating and deintercalating lithium ions, or capable of reversibly forming a lithium-containing compound by reacting with lithium ions.

[0060] The electrode mixture layer formed by including the slurry composition for an all-solid-state secondary battery of the present invention may contain a conductive material, and the conductive material is intended to ensure electrical contact between electrode active materials. When the conductive material is included, the electrical resistance of the electrode mixture layer can be effectively reduced. The slurry composition for an all-solid-state secondary battery according to the embodiment of the present invention has an ionic conductivity of 2.0×10 -2 S / CM, 2.5 x 10 -2 S / CM or higher, 3.0×10 -2 S / CM or more or 3.5 x 10 -2 It can be S / CM or more.

[0061] An all-solid-state secondary battery according to an embodiment of the present invention includes the slurry composition for an all-solid-state secondary battery.

[0062] The all-solid-state secondary battery includes a positive electrode, a solid electrolyte layer, and a negative electrode, and at least one of a positive electrode composite layer of the positive electrode, a negative electrode composite layer of the negative electrode, and a solid electrolyte layer may be included in the slurry composition for an all-solid-state secondary battery according to an embodiment of the present invention.

[0063] The all-solid-state secondary battery can adopt any of the structures, materials, and manufacturing methods of all-solid-state secondary batteries that are commonly used, and there are no particular limitations.

[0064] Specific examples of the present invention will be described below.

[0065] <Comparative Examples and Examples>

[0066] First, a binder and a first organic compound were mixed in the composition shown in Table 1 below to prepare a binder solution, and then an electrolyte having the composition shown in Table 1 below was added and mixed to synthesize a solid electrolyte.

[0067] In the table below 、L iPF6 / LiFSi 0.5 / 0.5M in EC / PC 1 / 2(v / v) as an organic electrolyte and a lithium salt, and VC 2% was used.

[0068] In addition, LSTP (Lithium Silicon Titanium Phosphate) was used as the inorganic electrolyte.

[0069] [Table 1]

[0070] <Experimental Example>

[0071] The total ion conductivity and electrochemical stability of the prepared solid electrolyte were measured, and the results are shown in FIGS. 1 and 2 and Table 2 below.

[0072] [Table 2]

[0073] 1, 2 and Table 2, it can be seen that the ionic conductivity and electrochemical stability of the examples of the present invention are significantly improved compared to the comparative examples.

Claims

1. A slurry composition for an all-solid-state secondary battery, comprising a binder and an organic electrolyte, the binder includes a polyimide-based compound, The organic electrolyte is at least one selected from linear or cyclic carbonates and esters; The slurry composition for an all-solid-state secondary battery does not contain an inorganic electrolyte. Slurry composition for all-solid-state secondary batteries.

2. The slurry composition for an all-solid-state secondary battery according to claim 1 , wherein the polyimide-based compound is a fluorinated polyimide (FPI).

3. The slurry composition for an all-solid-state secondary battery according to claim 1 , further comprising at least one selected from a first organic compound, a lithium salt, and an additive.

4. 3. The slurry composition for an all-solid-state secondary battery according to claim 2, wherein the fluorinated polyimide (FPI) is contained in an amount of 1 wt % to 20 wt % based on the total weight of the slurry composition for an all-solid-state secondary battery.

5. The slurry composition for an all-solid-state secondary battery according to claim 1 , wherein the binder does not include a polyvinylidene fluoride (PVdF)-based binder.

6. The slurry composition for an all-solid-state secondary battery according to claim 1 , further comprising at least one selected from an electrode active material and a conductive material.

7. Ion conductivity is 2.0 x 10 －２ The slurry composition for an all-solid-state secondary battery according to claim 1 , which has a viscosity of S / CM or more.

8. An all-solid-state secondary battery comprising the slurry composition for an all-solid-state secondary battery according to claim 1.

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