Solid state electrolyte and battery

Abstract

The application provides a solid-state electrolyte and a battery. The solid-state electrolyte comprises a polythiourethane, a polyacrylonitrile and a lithium salt, and the polythiourethane comprises a thiourethane structural unit. In the solid-state electrolyte provided by the application, the amino group in the thiourethane structural unit of the polythiourethane and the cyano group of the polyacrylonitrile form a hydrogen bond, so that the two have good compatibility. The blending of the polythiourethane and the polyacrylonitrile can effectively reduce the crystallinity of the polyacrylonitrile, improve the flexibility of the solid-state electrolyte, and at the same time make the solid-state electrolyte have good mechanical properties. In particular, the sulfur atom in the thiourethane structural unit of the polythiourethane helps to promote lithium ion transmission and improve ionic conductivity, and thanks to the interaction of the hydrogen bond formed by the polythiourethane and the polyacrylonitrile, the transmission rate of lithium ions can be further improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a solid-state electrolyte and a battery. BACKGROUND

[0002] Since commercialization, lithium ion batteries have been widely used in the fields of portable electronic devices and electric vehicles. Unlike traditional liquid lithium ion batteries, all-solid-state lithium batteries have the advantages of high specific energy, high safety performance, long cycle life, etc., and have become a research and development hotspot in the field of new chemical batteries in recent years.

[0003] The solid-state electrolyte includes a polymer solid-state electrolyte. Although the ionic conductivity of some polymer electrolytes in the existing polymer solid-state electrolyte can meet the use requirements of the solid-state electrolyte, the polymer electrolyte has the problem of too strong brittleness and accompanying warping, which affects the subsequent processing process of the battery.

[0004] Therefore, it is urgent to provide a solid-state electrolyte with mechanical properties and high ionic conductivity. SUMMARY

[0005] In view of the technical problem of low ionic conductivity and mechanical property of the existing solid-state electrolyte, the application provides a solid-state electrolyte and a battery.

[0006] To solve the above technical problem, on the one hand, the application provides a solid-state electrolyte, which comprises a polythiourethane, a polyacrylonitrile and a lithium salt, and the polythiourethane comprises a thiourethane structural unit.

[0007] Preferably, the solid-state electrolyte comprises 20%-40% of the polythiourethane, 40%-60% of the polyacrylonitrile and 20%-40% of the lithium salt, based on the total mass of the solid-state electrolyte being 100%.

[0008] Preferably, the glass transition temperature of the polythiourethane is 40℃-80℃.

[0009] Preferably, the weight average molecular weight of the polythiourethane is 10x10 4 g / mol-20x10 4 g / mol.

[0010] Preferably, the weight average molecular weight of the polyacrylonitrile is 20x10 4 g / mol-40x10 4 g / mol.

[0011] Preferably, the polythiourethane comprises a polymer formed by the participation of a diisocyanate compound and a thiol compound in polymerization.

[0012] Preferably, the molar ratio of the isocyanate groups of the diisocyanate compound and the mercapto groups of the thiol compound is 1:0.95-1:1.1.

[0013] Preferably, the diisocyanate compound comprises at least one of toluene diisocyanate, diphenyl methane diisocyanate, dicyclohexyl methane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate.

[0014] Preferably, the thiol compound comprises at least one of ethylene glycol bis-mercaptoacetate, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), inositol hexa(mercaptopropionate), and polythiol Capcure 3800.

[0015] Preferably, the lithium salt comprises at least one of lithium bistrifluoromethylsulfonimide, lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium perchlorate, lithium tetrafluorophosphate, lithium difluorophosphate, lithium bisoxalate borate, and lithium difluoro oxalate borate.

[0016] In another aspect, the present application provides a battery comprising a solid-state electrolyte film, wherein the solid-state electrolyte film comprises the solid-state electrolyte according to any one of the above.

[0017] Preferably, the thickness of the solid-state electrolyte film is 50 μm-200 μm.

[0018] In the solid-state electrolyte provided by the present application, the amino group in the thiourethane structure unit and the cyano group in the polyacrylonitrile form hydrogen bonds, so that the two have good compatibility. The blending of the polythiourethane and the polyacrylonitrile can effectively reduce the crystallinity of the polyacrylonitrile, improve the flexibility of the solid-state electrolyte, and at the same time make the solid-state electrolyte have good mechanical properties. In particular, the sulfur atom in the thiourethane structure unit can help to promote the transmission of lithium ions, improve the ionic conductivity, and further improve the transmission rate of lithium ions and the cycle performance of the battery due to the interaction of the hydrogen bonds formed by the polythiourethane and the polyacrylonitrile. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects solved by the present application more clearly understood, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0020] An embodiment of the present application provides a solid-state electrolyte, comprising a polythiourethane, a polyacrylonitrile and a lithium salt, wherein the polythiourethane comprises a thiourethane structure unit.

[0021] The amino group in the thio urethane structural unit in the polythio urethane and the cyano group in the polyacrylonitrile form a hydrogen bond in the solid-state electrolyte provided by the embodiment, so that the two have good compatibility. Blending the polythio urethane and the polyacrylonitrile can effectively reduce the crystallinity of the polyacrylonitrile, improve the flexibility of the solid-state electrolyte, and at the same time make the solid-state electrolyte have good mechanical properties. In particular, the sulfur atom in the thio urethane structural unit in the polythio urethane helps to promote lithium ion transmission and improve ionic conductivity, and thanks to the interaction of the hydrogen bond formed by the polythio urethane and the polyacrylonitrile, the transmission rate of lithium ions can be further improved, and the cycle performance of the battery can be improved.

[0022] In some embodiments, the solid-state electrolyte includes 20%-40% of the polythio urethane, 40%-60% of the polyacrylonitrile, and 20%-40% of the lithium salt, based on the total mass of the solid-state electrolyte being 100%.

[0023] By limiting the mass content of the polythio urethane, the polyacrylonitrile, and the lithium salt within the above range, the solid-state electrolyte has good flexibility and mechanical properties at the same time, and has high ionic conductivity. If the content of the polythio urethane is lower than the range, the flexibility of the solid-state electrolyte cannot be effectively improved, and at the same time, the transmission rate of lithium ions is reduced, and the ionic conductivity of the solid-state electrolyte is reduced. If the content of the solid-state electrolyte is higher than the range, the mechanical properties of the solid-state electrolyte are reduced, the penetration of lithium dendrites cannot be effectively inhibited, and the safety performance of the battery is affected.

[0024] Specifically, the mass content of the polythio urethane includes but is not limited to 20%, 23%, 26%, 29%, 32%, 35%, 38%, or 40%.

[0025] The mass content of the polyacrylonitrile includes but is not limited to 40%, 43%, 46%, 49%, 52%, 55%, 58%, or 60%.

[0026] The mass content of the lithium salt includes but is not limited to 20%, 23%, 26%, 29%, 32%, 35%, 38%, or 40%.

[0027] In some embodiments, the glass transition temperature Tg of the polythio urethane is 40-80℃. By limiting the glass transition temperature of the polythio urethane within the above range, the mechanical strength of the solid-state electrolyte film formed by the solid-state electrolyte can inhibit the penetration of lithium dendrites, and improve the safety performance of the battery.

[0028] The glass transition temperature is obtained by differential thermal analysis.

[0029] In some embodiments, the weight average molecular weight Mw of the polythio urethane is 10×10 4 -20×10 4g / mol. By limiting the weight average molecular weight of the polythiourethane to be within the above range, the glass transition temperature of the polythiourethane is controlled to meet the requirement of 40-80°C.

[0030] Specifically, the weight average molecular weight of the polythiourethane includes but is not limited to 10 x 10 4 g / mol, 11 x 10 4 g / mol, 12 x 10 4 g / mol, 13 x 10 4 g / mol, 14 x 10 4 g / mol, 15 x 10 4 g / mol, 16 x 10 4 g / mol, 17 x 10 4 g / mol, 18 x 10 4 g / mol, 19 x 10 4 g / mol, or 20 x 10 4 g / mol.

[0031] In some embodiments, the weight average molecular weight of the polyacrylonitrile is 20 x 10 4 - 40 x 10 4 g / mol.

[0032] Specifically, the weight average molecular weight of the polyacrylonitrile includes but is not limited to 20 x 10 4 g / mol, 23 x 10 4 g / mol, 26 x 10 4 g / mol, 29 x 10 4 g / mol, 32 x 10 4 g / mol, 35 x 10 4 g / mol, 38 x 10 4 g / mol, or 40 x 10 4 g / mol.

[0033] In some embodiments, the polythiourethane includes a polymer formed by polymerization of a diisocyanate compound and a thiol compound.

[0034] In some embodiments, the molar ratio of the isocyanate group of the diisocyanate compound to the mercapto group of the thiol compound is 1:0.95-1:1.1.

[0035] Specifically, the molar ratio of the isocyanate group of the diisocyanate compound to the mercapto group of the thiol compound includes but is not limited to 1:0.95, 1:1, or 1:1.1.

[0036] Further, the method for preparing the polythiourethane includes the following steps:

[0037] The thiol compound is placed in a reaction bottle, and before the reaction, 100-110℃ vacuum drying to remove water. After the temperature is reduced to 45-50℃, ensure that all raw materials are in a molten state, add the diisocyanate compound, mix well, then slowly add the catalyst, and react for 3-5h under a protective atmosphere to obtain a polythiourethane.

[0038] Further, the catalyst includes at least one of dibutyltin dilaurate, stannous octoate, bismuth iso-octoate, dibutyltin dimethoxide, dibutyltin diacetate, and dioctyltin dimaleate.

[0039] The catalyst is added in an amount of 0.2%-1.0% of the molar content of the diisocyanate compound to improve the reaction efficiency of the thiol compound and the diisocyanate compound.

[0040] The protective atmosphere is nitrogen or argon.

[0041] It should be noted that a chain extender can also be added during the preparation of the polythiourethane to further improve the flexibility of the solid-state electrolyte. Specifically, the chain extender includes but is not limited to an alcohol chain extender or an amine chain extender. The alcohol chain extender includes but is not limited to butanediol, hexanediol, glycerol, or trimethylolpropane. The amine chain extender includes but is not limited to 3,3'-dichloro-4,4'-diaminodiphenyl methane (MOCA), ethylenediamine (DA), N,N-dihydroxy(diisopropyl)aniline (HPA), or 2-imidazolidone.

[0042] In some embodiments, the diisocyanate compound includes at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI).

[0043] And / or, the thiol compound includes at least one of ethylene glycol bis-mercaptoacetate (GDMA), trimethylolpropane tris(3-mercaptopropionate) (TTMP), pentaerythritol tetra(3-mercaptopropionate) (PTMP), myo-inositol hexa(mercaptopropionate) (DHMP), and polythiol Capcure 3800.

[0044] In some embodiments, the lithium salt includes at least one of lithium bistrifluoromethanesulfonimide, lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium perchlorate, lithium tetrafluorophosphate, lithium difluorophosphate, lithium bisoxalate borate, and lithium difluoro oxalate borate.

[0045] In another aspect, an embodiment of the present application provides a battery including a solid-state electrolyte film, the solid-state electrolyte film including the solid-state electrolyte as claimed in any one of the above.

[0046] It should be noted that the battery can be a soft pack battery, a cylindrical battery, and a square battery.

[0047] In some embodiments, the thickness of the solid-state electrolyte film is 50-200 μm.

[0048] Specifically, the thickness of the solid-state electrolyte film includes but is not limited to 50 μm, 70 μm, 90 μm, 110 μm, 130 μm, 150 μm, 170 μm, 190 μm, or 200 μm.

[0049] In some embodiments, the method for preparing the solid-state electrolyte film includes the following steps:

[0050] The polyacrylonitrile, the polythiourethane, and the lithium salt are dissolved in a solvent to obtain a uniform mixed solution. Then, the solution is cast on a silica gel mold plate, left to stand to volatilize the solvent, and then placed in an oven to dry into a film to obtain the solid-state electrolyte film.

[0051] Further, the solvent can be selected from a polar aprotic solvent, and the polar aprotic solvent includes at least one of acetonitrile, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), propylene carbonate (PC), ethylene carbonate (EC), tetrahydrofuran (THF), 1,4-dioxane, and γ-butyrolactone (GBL).

[0052] The drying temperature is 30-90°C, and the drying mode can adopt gradient drying, specifically: in the first stage, vacuum drying at 30-40°C for 4-8h to preliminarily remove most of the solvent; and in the second stage, vacuum drying at 70-90°C for 12-24h to completely remove the residual solvent, so as to avoid the influence of residual solvent on the ionic conductivity of the electrolyte.

[0053] In some embodiments, an inorganic filler can be added to the solid-state electrolyte film to optimize the performance, and the inorganic filler can be selected from a lithium ion conductor filler or an insulating inorganic filler, wherein the lithium ion conductor filler includes at least one of LLZO, LLTO, LAGP, Li3PO4, LiTi2(PO4)3, Li2S, TiS2, and MoS2; the insulating inorganic filler includes at least one of Al2O3, SiO2, TiO2, ZrO2, MgO, ZnO, Si3N4, and AlN; the particle size of the inorganic filler is 10-200 nm, and the addition amount is 1%-10% of the total mass of the solid-state electrolyte, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0054] The battery further includes a positive electrode and a negative electrode, the positive electrode includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer is arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0055] The positive active material includes at least one of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobaltate (LCO), lithium manganate (LMO), lithium nickelate (LNO), ternary material (NCM, NCA), lithium-rich manganese-based (LMR), lithium nickel manganate (LNMO), lithium vanadium phosphate oxide (Li3V2(PO4)3, LiVOPO4).

[0056] The conductive agent includes at least one of carbon black (such as Ketjen black, acetylene black, superconducting carbon black), graphite (such as natural graphite, artificial graphite), carbon nanotube (such as single-walled carbon nanotube, multi-walled carbon nanotube), graphene, reduced graphene oxide; the addition amount of the conductive agent can be adjusted to 1%-5% of the total mass of the positive active material, for example, 1%, 2%, 3%, 4%, 5%, according to the positive conductive requirement.

[0057] The binder includes at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE); the addition amount of the binder is 2%-5% of the total mass of the positive active material, for example, 2%, 3%, 4%, 5%.

[0058] The negative electrode includes one of graphite negative electrode, silicon-oxygen negative electrode, silicon-carbon negative electrode, silicon negative electrode, tin negative electrode, tin oxide negative electrode, tin alloy negative electrode (Sn-Fe, Sn-Co, Sn-Cu), lithium metal negative electrode, lithium alloy negative electrode (Li-Ag, Li-Al, Li-Sn, Li-Mg, Li-Zn, Li-In, Li-Ga), lithium-free negative electrode.

[0059] The application is further described below by examples.

[0060] The solid-state electrolyte and the battery thereof disclosed in the application are specifically described.

[0061] Example 1

[0062] Solid-state electrolyte membrane

[0063] Polythiourethane: 210 g of ethylene glycol b-mercaptoacetate was placed in a reaction bottle, and before reaction, vacuum drying was performed at 105 DEG C for 3 h to remove water. After the temperature was reduced to 50 DEG C, 168 g of hexamethylene diisocyanate was added, and after uniform mixing, 0.38 g of di-n-butyltin dilaurate was slowly added, and reaction was performed under nitrogen protection conditions for 5 h to obtain polythiourethane.

[0064] 4 g of polyacrylonitrile, 3 g of polysulfur urethane, and 3 g of lithium bis-trifluoromethylsulfonimide were dissolved in 20 g of acetonitrile, and stirred at 25°C for 6 hours to obtain a homogeneous mixed solution. Then, the solution was cast on a silica gel mold plate, and first left to stand at 25°C for 24 hours to volatilize most of the solvent, and then placed in an oven at 80°C to dry into a film to obtain a solid electrolyte film.

[0065] The thickness of the solid electrolyte film was 100 pm.

[0066] Preparation of a negative electrode sheet

[0067] The negative electrode was a lithium metal negative electrode.

[0068] Preparation of a positive electrode sheet

[0069] NCM811 (active material), a conductive agent (carbon black / CNT), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2:3, and NMP was added to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil, and dried to obtain a positive electrode sheet.

[0070] Battery preparation

[0071] The negative electrode sheet, the positive electrode sheet, and the solid electrolyte film were assembled into a battery.

[0072] Examples 2-20

[0073] Examples 2-20 and most of the steps of Example 1 were the same, except that the formulations in Table 1 were used.

[0074] Example 21

[0075] Example 21 and most of the steps of Example 1 were the same, except that the molar ratio of hexamethylene diisocyanate to ethylene glycol bimerthiolate was 1:0.95.

[0076] Example 22

[0077] Example 22 and most of the steps of Example 1 were the same, except that the molar ratio of hexamethylene diisocyanate to ethylene glycol bimerthiolate was 1:0.9.

[0078] Example 23

[0079] Example 23 and most of the steps of Example 1 were the same, except that the molar ratio of hexamethylene diisocyanate to ethylene glycol bimerthiolate was 1:1.1.

[0080] Example 24

[0081] Example 24 and most of the steps of Example 1 were the same, except that the molar ratio of hexamethylene diisocyanate to ethylene glycol bimerthiolate was 1:1.2.

[0082] Comparative Example 1 - Comparative Example 2

[0083] Comparative Example 1 - Comparative Example 2 and Example 1 were the same in most steps, except that the formulations in Table 1 were used.

[0084] Comparative Example 3

[0085] Comparative Example 3 and Example 1 were the same in most steps, except that polyurethane was used instead of polythiourethane. The polyurethane was prepared using existing polyurethane synthesis methods with hexamethylene diisocyanate and 1,4-butanediol. The glass transition temperature of the polyurethane was 45°C.

[0086] Table 1

[0087]

[0088] The solid-state electrolytes and batteries prepared in the above examples and comparative examples were tested as follows.

[0089] 1. Mechanical property test: Tensile test was performed using a universal testing machine. According to the standard of ISO527-2, dumbbell-shaped samples were used with a parallel length of 20 mm, a width of 4 mm, and a sample thickness of 0.5 mm. The tensile speed was 50 mm / min during the test.

[0090] 2. Ionic conductivity test: The prepared polymer solid-state electrolyte film was tested for ionic conductivity at 25°C. The test method was alternating current impedance method, and the alternating current impedance was measured by an electrochemical workstation with a frequency range from 1000 KHz to 0.01 Hz and a perturbation voltage of 10 mV. The ionic conductivity data were calculated using the formula σ = L / (R x S), and the results are shown in Table 1. Wherein σ is the ionic conductivity, L is the thickness of the electrolyte film, R is the resistance value of the electrolyte film, and S is the contact area of the electrolyte film and the stainless steel electrode.

[0091] 3. Electrical performance test: The capacity retention rate was recorded under the following conditions: 25°C, 0.5 C charged to 4.0 V, cutoff current of 0.05 C, 1 C discharged to 3.0 V, and 300 cycles of cycling.

[0092] The test results are shown in Table 2 below.

[0093] Table 2

[0094]

[0095] It can be seen from the test results of the above examples and comparative examples that the tensile strength of the solid electrolyte film is improved and the elongation at break is reduced when the content of the polythiourethane is reduced. When the content of the polythiourethane is less than 20%, the ionic conductivity is low due to the inability to interact with the polyacrylonitrile. When the content of the polyacrylonitrile is increased, the tensile strength of the solid electrolyte film is improved and the elongation at break is reduced. When the content of the polyacrylonitrile is less than 40% or more than 60%, the ionic conductivity is low due to the inability to synergistically interact with the polythiourethane. When other types of isocyanate and thiol are used as raw materials to synthesize polythiourethane, the solid electrolyte film exhibits good mechanical properties, ionic conductivity, and capacity retention. When the molecular weight of the polyacrylonitrile is less than 20×10 4 g / mol, the mechanical strength of the solid electrolyte film is poor. When the molecular weight of the polyacrylonitrile is more than 40×10 4 g / mol, the compatibility of the polyacrylonitrile and the polythiourethane is poor, and the ionic conductivity of the solid electrolyte film is poor. When the solid electrolyte only uses polyacrylonitrile and lithium salt, the elongation at break of the solid electrolyte film is low. When the solid electrolyte only uses polythiourethane and lithium salt, the mechanical strength of the solid electrolyte film is not enough. When the solid electrolyte uses polyurethane instead of polythiourethane, the ionic conductivity of the solid electrolyte film is relatively low.

[0096] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte comprises polyurethane, polyacrylonitrile, and lithium salt, wherein the polyurethane comprises thiocarbamate structural units and hydrogen bonds are formed between the polyurethane and the polyacrylonitrile. Based on the total mass of the solid electrolyte as 100%, the solid electrolyte comprises 20%-40% polyurethane, 40%-60% polyacrylonitrile and 20%-40% lithium salt. The polysulfuron has a weight-average molecular weight of 10 × 10⁻⁶. 4 g / mol - 20 × 10 4 g / mol; The weight-average molecular weight of the polyacrylonitrile is 20 × 10⁻⁶. 4 g / mol - 40 × 10 4 g / mol.

2. The solid electrolyte according to claim 1, characterized in that, The glass transition temperature of the polysulfuric ester is 40℃-80℃.

3. The solid electrolyte according to claim 1, characterized in that, The polythiourethane comprises a polymer formed by the polymerization of diisocyanate compounds and thiol compounds.

4. The solid electrolyte according to claim 3, characterized in that, The molar ratio of the isocyanate group in the diisocyanate compound to the mercapto group in the thiol compound is 1:0.95-1:1.

1.

5. The solid electrolyte according to claim 3, characterized in that, The diisocyanate compounds include at least one of toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; And / or, the thiol compound includes at least one of ethylene glycol dimercaptoacetate, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate), inositol hexa(mercaptopropionate), and polythiol Capcure 3800.

6. The solid electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium bis(trifluoromethanesulfonate)imide, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium tetrafluorophosphate, lithium difluorophosphate, lithium bis(oxalate)borate, and lithium di(oxalate)borate.

7. A battery, characterized in that, Includes a solid electrolyte membrane, wherein the solid electrolyte membrane comprises the solid electrolyte as described in any one of claims 1-6.

8. The battery according to claim 7, characterized in that, The thickness of the solid electrolyte membrane is 50 μm-200 μm.

Images