Preparation method of asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte and low-temperature application

Abstract

The application discloses an asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte (CPE) and a preparation method thereof. A fiber film substrate is prepared by using an electrostatic spinning technology, a strong polar functional group (-CN) is used to improve lithium ion transmission kinetics, and an in-situ polymerization process is used for selective adsorption, so that a local conjugated polymer solid electrolyte nanolayer is formed on ceramic oxide particles. A softened polymer-rich layer and a ceramic particle layer on the anode side can effectively improve interface stability, inhibit dendrite growth and promote lithium ion transmission. In addition, the CPE in-situ encapsulated with non-flammable phosphate exhibits excellent flame retardancy. Therefore, the lithium metal battery based on the CPE exhibits excellent cycles in a wide temperature range of -20 to 80 DEG C. The asymmetric CPE designed by the strategy shows great potential in promoting the development of high-energy-density and safe lithium metal batteries, opens up a new way for solving the LALZO / electrode interface problem, and is helpful to the commercialization and application of wide-temperature-range SSLMBs.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation method of wide-temperature-range non-flammable composite solid-state electrolyte, in particular to a preparation method of asymmetric double-layer wide-temperature-range non-flammable composite solid-state electrolyte. BACKGROUND

[0002] Electrochemical energy storage devices are crucial for achieving decarbonization goals. Lithium-ion batteries dominate the consumer electronics market, such as electric vehicles, due to their ultra-high energy density. However, traditional liquid electrolytes are corrosive and thermally unstable. Therefore, SSE is a reliable alternative to liquid electrolytes to ensure the safety of batteries. In general, common solid electrolytes are classified into solid inorganic electrolytes (SIEs), solid polymer electrolytes (SPEs), and composite polymer electrolytes (CPEs). Among them, as a combination of SIE and SPE, CPE inherits the advantages of inorganic and polymer electrolytes and is considered an effective competitor for current high-performance SSLMBs.

[0003] Previous studies have shown that the presence of a small amount of ceramic oxide can reduce crystallization and improve the ionic conductivity of CPE. It is worth noting that limited number of ceramic particles cannot effectively improve the mechanical ability of CPE to suppress lithium dendrites. Once dominated by ceramics, the high mechanical strength of CPE can be considered as a mechanical barrier to suppress lithium dendrites. However, these CPEs can severely reduce the overall conductivity due to the enhanced electrolyte / electrode interface resistance. Therefore, the special structural design of CPEs that can both suppress the growth of lithium dendrites and improve the lithium ion transport of SSLMBs will be of great significance. In addition, in the most in-depth CPEs, polymer solid electrolytes and polymer / ceramic composites are usually flammable, and safety issues are ignored. Therefore, it is urgent to develop flame-retardant CPEs that can enhance mechanical properties and regulate ion distribution to suppress lithium dendrite growth and achieve high-performance SSLMBs. SUMMARY

[0004] In view of the above problems existing in the prior art, the purpose of the present application is to provide a preparation method and application of an asymmetric double-layer wide-temperature-range non-flammable composite solid-state electrolyte. The composite solid-state electrolyte prepared by the method has a special asymmetric structure, flame retardation, and excellent low-temperature performance. The CPE is composed of a nanofiber film (PCN), a flame retardant additive (TPPO), and an ion-conducting composite polymer electrolyte (silane coupling agent functionalized aluminum-doped lithium lanthanum zirconium oxide, poly(ethylene glycol) diacrylate, and bis(trifluoromethylsulfonyl) lithium) imide). In the preparation process, a cyanofiber film substrate prepared by electrospinning technology is used. The strong polar functional group (-CN) improves the lithium ion transport kinetics, improves the battery rate discharge performance and cycle performance at high rates, and selectively adsorbs during the subsequent in-situ polymerization process to form a local conjugated polymer solid-state electrolyte nanolayer on the ceramic oxide particles. Among them, the softened polymer-rich layer can effectively wet the cathode, giving excellent interface stability. The ceramic particles on the anode side can effectively inhibit the growth of dendrites and promote the transport of lithium ions. In addition, the in-situ encapsulation of non-flammable phosphate CPE exhibits excellent flame retardancy. This makes the CPE have high ionic conductivity, considerable Li + transfer number, high interfacial compatibility, and excellent flame retardancy. The assembled Li / NCM811 / lithium battery can still provide excellent cycle performance at a low temperature of -20℃.

[0005] The technical solutions of the present application are as follows:

[0006] The present application provides a preparation method of an asymmetric double-layer wide-temperature-range non-flammable composite solid-state electrolyte, characterized in that the composite solid-state electrolyte comprises a nanofiber film substrate; a silane coupling agent (MPS) functionalized active ceramic, poly(ethylene glycol) diacrylate (PEGDA), a phosphorus-based flame retardant additive, and a conductive lithium salt.

[0007] Further, in the above technical solution, the nanofiber film substrate material is one or more of cyanopolymer (PCN), poly(vinylidene fluoride-CO-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF). This gives the composite electrolyte a more optimal functional group synergy and optimizes the comprehensive performance.

[0008] Further, in the above technical solution, the active ceramic in the silane coupling agent (MPS) functionalized active ceramic includes one of aluminum-doped lithium lanthanum zirconium oxide, lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium niobium oxide, titanium aluminum lithium phosphate, and lithium lanthanum titanium oxide.

[0009] Further, in the above technical solution, the polymer electrolyte is PEGDA containing a carbon-carbon double bond, and the average molecular weight of the poly(ethylene glycol) diacrylate (PEGDA) is 600.

[0010] Further, in the above technical solution, the flame retardant additive includes one of tributyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, etc. in the phosphorus-based flame retardant.

[0011] Further, in the above technical solution, the conductive lithium salt includes one of LiTFSI, LiPF6, LiBF4, and LiClO4.

[0012] The application provides a preparation method of the above asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte, including the following steps: 1) mixing cyanopolymer in a certain proportion in DMF, electrospinning to construct a 3D composite fiber structure, and constructing a dense base layer by using heat compression to thin to obtain a cyanopolymer (PCN) nanofiber membrane base.

[0013] 2) mixing silane coupling agent (MPS) functionalized active ceramic and poly(ethylene glycol) diacrylate (PEGDA), adding a certain amount of liquid electrolyte containing conductive lithium and phosphorus-based flame retardant additive, adding an initiator after uniform dispersion to obtain a precursor solution, coating the precursor solution on the cyanopolymer (PCN) nanofiber membrane base to construct an asymmetric electrolyte, and heating in an argon oven at 70°C for 2 h to complete the polymerization reaction.

[0014] Further, in the above technical solution, the concentration of conductive lithium in the liquid electrolyte is 2-4 M, the content of the phosphorus-based flame retardant additive is 0.1-1 wt%, the content of fluoroethylene carbonate FEC is 5-10 wt%, and the volume ratio of ethylene carbonate EC to diethyl carbonate DEC is 1-2:1-2.

[0015] Further, in the above technical solution, the ratio of poly(ethylene glycol) diacrylate (PEGDA) to liquid electrolyte is 1:3-1:5 in mass ratio.

[0016] Further, in the above technical solution, the amount of silane coupling agent (MPS) functionalized active ceramic is 10-20 wt% of PEGDA.

[0017] The present application provides an asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte and a preparation method thereof. The strong polar functional group (-CN) carried by the cyan fiber substrate improves lithium ion transmission kinetics, improves battery rate discharge performance and cycle performance at high rates, and the softened polymer-rich layer can effectively wet the cathode, imparting excellent interface stability. The LALZO-rich layer not only has the characteristics of accelerating ion migration kinetics, but also adjusts uniform Li deposition during charging and discharging, forming a stable electrolyte / Li anode interface, thereby synergistically inhibiting the growth of lithium dendrites. In addition, the in-situ encapsulated non-flammable phosphate CPE exhibits excellent flame retardancy. This makes the CPE exhibit excellent performance, high ionic conductivity, considerable Li + transfer number, mechanical flexibility, and excellent flame retardancy. The assembled Li / NCM811 / lithium battery can still provide excellent cycle performance at a low temperature of -20°C. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The scanning electron microscope images of the nanofiber substrate films prepared in Examples 1, 2, and 3 of the present application are shown.

[0019] Figure 2 The cycle diagram of the asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte prepared in Example 1 and Example 3 of the present application is shown.

[0020] Figure 3 The ionic conductivity of the asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte in Example 3 at 25-100°C.

[0021] Figure 4 The CA curve of the asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte prepared in Example 3.

[0022] Figure 5 The cycle performance of the asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte in Example 3 at -20°C.

[0023] Figure 6 The flame retardancy of the asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte in Example 3. DETAILED DESCRIPTION

[0024] Example 1 (without nanometer M-LALZO powder)

[0025] The application discloses a preparation method of an asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte, and has the characteristics that the composite solid electrolyte comprises a cyanopolymer (PCN) nanofiber membrane base, silane coupling agent (MPS) functionalized aluminum-doped lithium lanthanum zirconium oxide (M-LALZO) active ceramic, poly(ethylene glycol) diacrylate (PEGDA), additive triphenylphosphine oxide (TPPO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The specific steps are as follows:

[0026] Preparation of a cyanopolymer (PCN) nanofiber membrane

[0027] PCN is dispersed in DMF to configure a polymer spinning solution with a concentration of 13%, and stirring is performed for 12 h to obtain a uniform spinning solution for electrospinning. The spinning solution is transferred to a syringe provided with a stainless steel needle with a diameter of 20 mm. In the electrospinning process, a high voltage of 15 kv, a negative pressure of -2.25 kv and a receiving distance of 18 cm are adopted, the ejection speed is 1 mL / h, and the spinning time is 4 h. Finally, the electrospun fibers are collected on a smooth kraft paper which is automatically wound. After a heat pressing process at 100 DEG C, an electrospun nanofiber membrane with a thickness of 15 mu m is obtained, as shown in Figure 1 .

[0028] Preparation of M-LALZO active ceramic

[0029] First, 48 mL of isopropyl alcohol and 19 mL of glycerol are mutually soluble, 0.05 mmol of Al(NO3)3.9H2O is added, stirring is performed for 30 min until Al(NO3)3.9H2O is dissolved, 1 mL of an aqueous solution in which 0.4 mmol of Zr(NO3)4.3H2O and 0.6 mmol of La(NO3)3.6H2O are sequentially dissolved is added, and stirring is continuously performed for 2 h until the solution becomes transparent. Then, the solution is transferred into a 100 mL polytetrafluoroethylene reaction kettle, and is kept in an oven at 180 DEG C for 16 h. After the reaction is completed, the generated precipitate is taken out, washed with anhydrous ethanol for 3 times, and is placed in a 60 DEG C oven for constant temperature drying for 24 h. After that, the dried powder is taken out, is ground and mixed with 1.44 mmol (20% excess) of LiOH.H2O, and is placed in a muffle furnace, and is calcined at 800 DEG C for 3 h, and the temperature rising rate is 5 DEG C / min. After cooling, the product is taken out and is ground to obtain a nanofiller LALZO.

[0030] M-LALZO was prepared by ultrasonic method. First, 1 g of bulk LALZO was mixed with 180 mL of IPA for 2 h until a uniform suspension was formed. 20 mL of the stirring 2 h MPS and IPA mixed solution (mass ratio of MPS to IPA was 1:9) was added to the above suspension, and the dispersion was continued for 4 h. Finally, the complete suspension was filtered and dried under vacuum at 100 °C for 48 h to obtain M-LALZO. The hydroxylation occurred during the initial ultrasonic or stirring of LALZO and MPS. After mixing, the hydroxyl groups between them further dehydrated under the action of ultrasonic, and LALZO and MPS could be successfully grafted.

[0031] Preparation of in-situ polymerized composite solid-state battery

[0032] 0 wt% of nano M-LALZO powder, monomer PEGDA (mass ratio of 1:5 to liquid electrolyte), AIBN (0.5 wt% of PEGDA monomer) were added to the liquid electrolyte (3M LiTFSI + 0.5 wt% TPPO + 8 wt% FEC + EC:DEC volume ratio of 1~2:1~2), and stirred vigorously for 6 h to form a uniform solution. These mixtures were quickly injected into the assembled 2025 coin-type battery until the nanofiber membrane (PCN) was completely penetrated. The battery was stored at 70 °C for 2 h to ensure complete polymerization. The above experiment was carried out in an argon-filled glove box (Mikrouna, H2O, O2≤0.1 ppm).

[0033] Figure 2 The cyclic diagram showing the lithium | electrolyte | lithium battery charged and discharged at a current density of 0.1 mA cm -2 The overpotential of Example 3 is significantly lower than that of Example 1, which indicates that the addition of M-LALZO effectively suppresses the side reaction and promotes uniform lithium plating and stripping in the solid-state battery.

[0034] Example 2

[0035] A preparation method of an asymmetric double-layer wide-temperature-range non-flammable composite solid-state electrolyte, characterized in that the composite solid-state electrolyte comprises a cyanopolymer (PCN) nanofiber membrane substrate; a silane coupling agent (MPS) functionalized aluminum-doped lithium lanthanum zirconium oxide (M-LALZO) active ceramic, poly(ethylene glycol) diacrylate (PEGDA), an additive triphenylphosphine oxide (TPPO), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The specific steps are as follows:

[0036] Preparation of cyanopolymer (PCN) nanofiber membrane

[0037] PCN was dispersed in DMF to configure a polymer spinning solution with a concentration of 13%, and stirred for 12 h to obtain a uniform spinning solution for electrospinning. The spinning solution was transferred to a syringe equipped with a stainless steel needle with a diameter of 20 mm. During the electrospinning process, a high voltage of 15 kv, a negative pressure of -2.25 kv and a receiving distance of 18 cm were adopted, the injection speed was 1 mL / h, and the spinning time was 4 h. Finally, the electrospun fibers were collected on a smooth kraft paper with automatic winding. After a heat pressing process at 100°C, an electrospun nanofiber membrane with a thickness of 15 μm was obtained.

[0038] Preparation of M-LALZO active ceramic

[0039] First, 48 mL of isopropyl alcohol and 19 mL of glycerol were miscible, then 0.05 mmol of Al(NO3)3·9H2O was added, and stirred for 30 min until Al(NO3)3·9H2O was dissolved. Then 1 mL of aqueous solution in which 0.4 mmol of Zr(NO3)4·3H2O and 0.6 mmol of La(NO3)3·6H2O were sequentially dissolved was added, and stirring was continued for 2 h until the solution became transparent. Then it was transferred to a 100 mL polytetrafluoroethylene reaction kettle and kept in an oven at 180°C for 16 h. After the reaction was completed, the generated precipitate was taken out, washed with anhydrous ethanol for 3 times, and placed in a 60°C oven for constant temperature drying for 24 h. Then the dried powder was taken out, mixed with 1.44 mmol (20% excess) of LiOH·H2O, and placed in a muffle furnace for calcination at 800°C for 3 h with a heating rate of 5°C / min. After cooling, it was taken out and ground to obtain the nano-filler LALZO.

[0040] M-LALZO was prepared by ultrasonic method. First, 1 g of bulk LALZO was mixed with 180 mL of IPA and dispersed for 2 h until a uniform suspension was formed. 20 mL of MPS mixed solution stirred for 2 h was added to the above suspension (the mass ratio of MPS to IPA was 1:9), and the dispersion was continued for 4 h. Finally, the complete suspension was filtered and vacuum dried at 100°C for 48 h to obtain M-LALZO. Hydroxylation occurs during initial ultrasonic or stirring of LALZO and MPS. After mixing, the hydroxyl groups between them further dehydrate under the action of ultrasonic, and LALZO and MPS can be successfully grafted.

[0041] Preparation of in-situ polymerization composite solid-state battery

[0042] A solution of 10 wt% nanofibrous PCN, monomer PEGDA (1:5 mass ratio with liquid electrolyte), AIBN (0.5 wt% of PEGDA monomer) was added to the liquid electrolyte (3 M LiTFSI + 0.5 wt% TPPO + 8 wt% FEC + EC:DEC volume ratio 1-2:1-2) and stirred vigorously for 6 h to form a homogeneous solution. These mixtures were quickly injected into the assembled 2025 coin-type battery until the nanofibrous membrane (PCN) was completely penetrated. The battery was stored at 70 °C for 2 h to ensure complete polymerization. The above experiments were carried out in an argon-filled glove box (Mikrouna, H2O, O2≤0.1 ppm).

[0043] Example 3

[0044] The application discloses a preparation method of an asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte, and belongs to the technical field of solid electrolyte materials.

[0045] Preparation of a nanofibrous PCN membrane

[0046] A polymer spinning solution with a concentration of 13% was prepared by dispersing the PCN in DMF and stirring for 12 h to obtain a uniform spinning solution for electrospinning. The spinning solution was transferred to a syringe equipped with a stainless steel needle with a diameter of 20 mm. During the electrospinning process, a high voltage of 15 kv, a negative pressure of -2.25 kv, and a receiving distance of 18 cm were adopted, the injection speed was 1 mL / h, and the spinning time was 4 h. Finally, the electrospun fibers were collected on a smooth kraft paper with automatic winding. After a heat pressing process at 100 °C, a nanofibrous membrane with a thickness of 15 μm was obtained.

[0047] Preparation of M-LALZO active ceramic

[0048] First, 48 mL of isopropyl alcohol and 19 mL of glycerol were miscible, then 0.05 mmol of Al(NO3)3·9H2O was added, and stirred for 30 min until Al(NO3)3·9H2O was dissolved, then 1 mL of an aqueous solution of 0.4 mmol of Zr(NO3)4·3H2O and 0.6 mmol of La(NO3)3·6H2O was added in turn, and continued to stir for 2 h until the solution became transparent, and then transferred to a 100 mL polytetrafluoroethylene reactor, and kept in an oven at 180°C for 16 h. After the reaction was completed, the generated precipitate was taken out, washed with anhydrous ethanol for 3 times, and placed in a 60°C oven for constant temperature drying for 24 h. Then the dried powder was taken out, mixed with 1.44 mmol (20% excess) of LiOH·H2O, and placed in a muffle furnace, and calcined at 800°C for 3 h with a heating rate of 5°C / min. After cooling, it was taken out and ground to obtain the nano-filler LALZO.

[0049] M-LALZO was prepared by ultrasonic method. First, 1 g of bulk LALZO was mixed with 180 mL of IPA and dispersed for 2 h until a uniform suspension was formed. 20 mL of MPS and IPA mixed solution stirred for 2 h was added to the above suspension (the mass ratio of MPS to IPA was 1:9), and continued to disperse for 4 h. Finally, the complete suspension was filtered and vacuum dried at 100°C for 48 h to obtain M-LALZO. Hydroxylation occurs during initial ultrasonic or stirring of LALZO and MPS. After mixing, the hydroxyl groups between them further dehydrate under the action of ultrasonic, and LALZO and MPS can be successfully grafted.

[0050] Preparation of in-situ polymerized composite solid-state battery

[0051] 20wt% of nano-M-LALZO powder, monomer PEGDA (mass ratio of 1:5 to liquid electrolyte), AIBN (0.5wt% of PEGDA monomer) were added to the liquid electrolyte (3M LiTFSI+0.5wt% TPPO+8wt% FEC+EC:DEC volume ratio of 1~2:1~2), and stirred vigorously for 6 h to form a uniform solution. These mixtures were quickly injected into the assembled 2025 coin-type battery until the nanofiber membrane (PCN) was completely penetrated. The battery was stored at 70°C for 2 hours to ensure complete polymerization. The above experiment was carried out in an argon-filled glove box (Mikrouna, H2O, O2≤0.1 ppm).

[0052] As shown in Figures 3-5 , CHI760E electrochemical workstation was used to perform EIS test of solid-state battery at a temperature of 25~100°C, and the asymmetric double-layer wide-temperature-range non-flammable composite solid-state electrolyte showed high ionic conductivity (8.5×10-4 ) and high Li + The number of transits (0.68). In the battery performance test, the constant current charge and discharge test was used to evaluate the electrochemical behavior, energy storage and release capacity of the battery. The performance test of the number of cycles was carried out in a low temperature test cabinet at-20℃ with a charge and discharge current density of 0.3C. It can be seen that the assembled Li / NCM811 / lithium battery can still provide excellent cycle performance at a low temperature of-20℃.

[0053] As Figure 6 shown, the flame retardancy of the asymmetric double-layer wide temperature range non-flammable composite solid electrolyte was verified, and no serious combustion and obvious deformation was observed in the figure, proving its good flame retardancy. The results show that this electrolyte provides a new good solution to solve the safety problem of electrolyte.

Claims

1. An asymmetric, double-layered, wide-temperature-range, non-flammable composite solid electrolyte, characterized in that, The composite solid electrolyte includes a nanofiber membrane substrate; silane coupling agent MPS functionalized active ceramic; poly(ethylene glycol) diacrylate PEGDA; phosphorus-based flame retardant additives; and conductive lithium salt. The nanofiber membrane substrate is made of cyanopolymer PCN; the nanofiber membrane substrate is a 3D composite fiber structure constructed by electrospinning, and a dense base layer is constructed by hot pressing composite thinning to obtain the cyanopolymer PCN nanofiber membrane substrate. The active ceramic in the silane coupling agent MPS functionalized active ceramic includes aluminum-doped lithium lanthanum zirconium oxide. The flame retardant additive includes one of the phosphorus-based flame retardants: tributyl phosphate, triphenyl phosphate, and dimethyl methylphosphonate. The amount of the silane coupling agent MPS functionalized active ceramic is 10-20 wt% of poly(ethylene glycol) diacrylate PEGDA.

2. The electrolyte according to claim 1, characterized in that, The average molecular weight of the poly(ethylene glycol) diacrylate PEGDA is 600.

3. The electrolyte according to claim 1, characterized in that, The conductive lithium salt includes one of LiTFSI, LiPF6, LiBF4, and LiClO4.

4. A method for preparing an asymmetric bilayer wide-temperature-range non-flammable composite solid electrolyte according to any one of claims 1 to 3, characterized in that, Includes the following steps: 1) A cyano polymer is mixed and dissolved in DMF in a certain proportion, and a 3D composite fiber structure is constructed by electrospinning. A dense base layer is constructed by hot pressing composite thinning to obtain a cyano polymer PCN nanofiber membrane substrate. 2) The silane coupling agent MPS functionalized active ceramic was mixed with poly(ethylene glycol) diacrylate PEGDA, and a certain amount of liquid electrolyte containing conductive lithium salt and phosphorus flame retardant additives was added. After being dispersed evenly, an initiator was added to obtain a precursor solution. The precursor solution was coated on a cyano polymer PCN nanofiber membrane substrate to construct an asymmetric electrolyte. The polymerization reaction was completed by heating in an argon oven at 70°C for 2 h.

5. The method for preparing an asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte according to claim 4, characterized in that, The liquid electrolyte contains a conductive lithium salt concentration of 2-4M, a phosphorus-based flame retardant additive content of 0.1-1wt%, a fluoroethylene carbonate (FEC) content of 5-10wt%, and a solvent consisting of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1-2:1-2.

6. The method for preparing an asymmetric double-layer wide-temperature-range non-flammable composite solid electrolyte according to claim 5, characterized in that, The ratio of the poly(ethylene glycol) diacrylate (PEGDA) to the liquid electrolyte is 1:3 to 1:5 by mass.

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