Titanium lithium aluminum phosphate solid electrolyte polymer interface modification and preparation method thereof

Abstract

The invention discloses a titanium lithium aluminum phosphate solid electrolyte polymer interface modification method and a preparation method thereof. The method comprises the following steps: firstly, selecting LITFSI (lithium ion conductor), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) and DMSO (dimethyl sulfoxide) liquid, and mixing to form PVDF-HFP-based polymer mixed liquid; then, the PAN film doped with titanium lithium aluminum phosphate powder is uniformly coated with the mixed solution through a press coating method, and the PVDF-HFPPAN film is obtained through drying treatment. And cutting the membrane, placing the cut membrane on two sides of a ceramic chip solid electrolyte, assembling an all-solid-state battery, activating at 40-80 DEG C until the polymer is attached to a metal lithium negative electrode and the surface of the solid electrolyte in a gel state, and cooling to finally obtain the solid electrolyte with a PVDF-HFPPAN coated LATP coated PVDF-HFPPAN sandwich structure. The modified solid-state electrolyte membrane can effectively inhibit the interface reaction of LATP on the lithium negative electrode side and enhance the wettability of the positive and negative electrode interface, thereby meeting the cycle performance requirement of the solid-state battery under the normal temperature condition.

Description

Technical Field

[0001] The present invention belongs to the field of solid-state lithium metal batteries, and specifically relates to a lithium aluminum titanium phosphate solid-state electrolyte polymer interface modification and a preparation method thereof. Background Art

[0002] Solid-state lithium metal batteries are receiving great attention from the industry due to their excellent energy density and safety. The high energy density of this battery is due to the extremely high theoretical capacity (3860mAh / g) of lithium metal, the extremely low reduction potential (-3.04V), and the low density (0.53g / cm 3 ). At the same time, the high safety of solid-state lithium metal batteries is due to the use of inorganic solid electrolytes, which effectively avoids the risks of leakage, evaporation and combustion of liquid electrolytes. 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP) solid electrolytes are favored due to their excellent moisture resistance, which is superior to other inorganic electrolytes such as sulfides, halides, hydrides, and garnet-structured Li7La3Zr2O 12 (LLZO). Compared with LLZO, LATP lacks the natural passivation layer formed by Li2CO3. Nevertheless, LATP faces degradation problems when in contact with lithium metal anode due to its internal Ti 4+ The degradation is caused by the redox activity of LATP and lithium. This degradation causes the accumulation of passivation byproducts such as Li2O on the LATP surface, which in turn hinders the conduction of lithium ions and reduces the battery capacity. Chemical reactions are usually accompanied by changes in physical volume, and this feature is particularly significant at the contact interface between LATP and lithium metal. This interfacial reaction will generate internal stress inside LATP, severely weaken the mechanical strength of LATP ceramic particles, and affect its contact quality with the electrode. In order to improve the stability of the LATP / Li interface, an artificial buffer layer must be used to inhibit the Ti 4+ The side reactions during the reduction process are suppressed, thereby protecting the electrolyte and maintaining its performance.

[0003] Over the past few decades, researchers have developed a variety of artificial buffer layer technologies aimed at suppressing interfacial side reactions between solid electrolytes and lithium metal. For example, inorganic materials such as ZnO (Adv. Energy Mater. 9 (2019) 1901604), Al2O3 (Nat. Mater. 16 (2017) 572-579) and BN (Joule 3 (2019) 1510-1522) have been tried for this purpose. However, these inorganic layers have some limitations: they may be chemically or spatially incompatible with lithium metal, or need to be kept extremely thin to ensure ionic conductivity at the interface. The preparation of such thin layers usually relies on expensive equipment to precisely control the thickness and crystallinity of the layer. Compared with inorganic layers, macromolecular organic buffer layers have obvious advantages: they are easy to operate, low cost, and easy to control thickness. This is mainly due to the in-situ polymerization ability and fluid properties of macromolecular materials. For example, polymers with inherent nanoporosity (Adv. Funct. Mater. 29 (2019) 1805996) and polyacrylonitrile (Acta 56 (2011) 6474-6480) have been used to improve the compatibility between LATP and lithium metal. In addition, some polymer strategies have also been shown to improve the ionic conductivity of LATP-based composite electrolytes (Angew. Chem. Int. Ed. 60 (2021) 24668-24675). Among them, the most commonly used is to deposit a plastic polymer electrolyte PEO on the surface of the electrolyte. However, PEO has low ionic conductivity at room temperature, insufficient mechanical strength, may decompose at high temperatures, and has a narrow electrochemical window, which limits its performance in solid-state batteries.

[0004] Therefore, the development of a new polymer interface layer is crucial for LATP solid-state electrolytes. It will improve the compatibility between electrolytes and electrodes, reduce interfacial side reactions, extend battery life, and increase energy density, providing key support for the commercialization of solid-state lithium metal batteries. It is of great significance to the development of efficient and safe battery technology. Summary of the invention

[0005] The purpose of the present invention is to provide a novel method for sustained-release modification of the solid electrolyte / metal lithium interface and its application to improve the interface stability between the solid electrolyte and the lithium metal negative electrode, thereby improving the overall comprehensive performance of the solid-state lithium metal battery. In order to achieve the above purpose, the present invention adopts the following technical scheme:

[0006] A lithium aluminum titanium phosphate solid electrolyte polymer interface modification and a preparation method thereof, characterized in that it comprises the following steps:

[0007] S1: Take 4-12 parts by weight of lithium bis(trifluoromethylsulfonyl)imide (LITFSI), 6-18 parts by weight of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), and 10-20 mL of dimethyl sulfoxide (DMSO), mix them, and vigorously stir at 60° C. to obtain a PVDF-HFP-based polymer mixed solution;

[0008] S2: A certain amount of polyacrylonitrile (PAN) matrix was completely dissolved in an appropriate amount of N, N-dimethylformamide (DMF) solvent to prepare a 10% polyacrylonitrile solution. After obtaining a light yellow transparent solution, the LATP powder in S1 was weighed and added to the above solution to prepare electrospinning solutions with mass fractions of 0%, 5%, 10% and 20% in sequence.

[0009] S3: The spinning solutions of different concentrations obtained in S2 are used to prepare PAN@LATP composite membranes by electrospinning;

[0010] S4: coating the PVDF-HFP based polymer mixture on the composite membrane in S2 by pressure coating, and vacuum drying to obtain a PVDF-HFP|PAN@LATP membrane;

[0011] S5: Place the PVDF-HFP|PAN@LATP membrane cut pieces described in S4 on both sides of the LATP electrolyte to assemble into an all-solid-state battery. Activate the all-solid-state battery with a protective layer on the surface at 40-80°C until the polymer is attached to the electrolyte and the positive and negative electrode surfaces in a gel state;

[0012] Preferably, in step S1, the mass ratio of PVDF-HFP to LITFSI is 3:2, and the concentration of LITFSI is 1-5M.

[0013] Preferably, the LATP powder in step S2 is synthesized by a hydrothermal method and has a particle size between 500-600 nm.

[0014] Preferably, in step S3, the spinning solution is magnetically stirred at 30-60°C for 10-24h, and the electrospinning speed and time are set to be 0.6mL h -1 and 7 hours.

[0015] Preferably, the drying temperature in step S4 is 30-60° C., and the drying time is 6-12 hours.

[0016] Compared with the prior art, the advantages of the present invention are as follows:

[0017] (1) The process used is relatively simple, has low equipment requirements, is easy to apply on a large scale, is environmentally friendly, and has low cost. (2) Unlike the prior art method of using PEO-based polymer solid electrolytes to modify the interface of LATP, the present invention not only improves the concentration of the electrolyte, but also achieves effective regulation of the solvation structure through a carefully designed non-solvated solid framework. This improvement significantly enhances the interfacial compatibility between the lithium negative electrode and the high-voltage positive electrode material. In addition, the traditional PEO-based electrolyte has the problem of low lithium ion migration number, but in the present invention, the solvation structure of the electrolyte is significantly optimized under ultra-high salt concentration conditions, which promotes the conduction efficiency of lithium ions. The inorganic LATP particles contained in the composite membrane help to improve the mechanical properties and thermal stability, and effectively inhibit the growth of lithium dendrites. These characteristics not only solve the problems of low ionic conductivity and lithium ion migration number at room temperature, but also provide new solutions for improving the performance and enhancing the safety of all-solid-state lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the electrochemical impedance spectroscopy of the all-solid-state lithium symmetric battery before cycling;

[0019] Figure 2 For all-solid-state lithium symmetric batteries at 0.2 mA cm -2 Galvanostatic cycle diagram under current density; DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example 1

[0022] (1) LiNO3·H2O, Al(NO3)3·9H2O, H3PO4, and (Ti(OC4H9)4) powders were weighed in a molar ratio of 1.3:0.3:1.7:3 and subjected to a hydrothermal reaction at 180°C for 10 h to synthesize Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP) ceramic powder was ball-milled at 500rpm for 6h and pressed at 500Mpa to obtain a ceramic embryo, which was then sintered at 800℃ for 6h to obtain a ceramic electrolyte sheet. The LATP ceramic sheet was polished with 1000-mesh metallographic sandpaper for later use.

[0023] (2) Add polyvinylidene fluoride-hexafluoropropylene and lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 3:2 into dimethyl sulfoxide and stir at 60° C. until they are completely dissolved.

[0024] (3) A certain amount of polyacrylonitrile (PAN) matrix is ​​completely dissolved in an appropriate amount of N,N-dimethylformamide (DMF) solvent to prepare a 10% polyacrylonitrile solution. After obtaining a light yellow transparent solution, the LATP powder in step 1 is weighed and added to the above solution to prepare an electrospinning solution with a mass fraction of 20%.

[0025] (4) The PVDF-HFP-based polymer mixture is coated on the composite membrane in step 2 by pressure coating, and vacuum dried at 60° C. for 10 h to obtain a PVDF-HFP|PAN membrane.

[0026] (5) The PVDF-HFP|PAN membrane described in step 4 is cut into 14 mm original sheets by a sheet cutter, transferred to a glove box and encapsulated on both sides of the LATP electrolyte to assemble into an all-solid-state battery. The all-solid-state battery with a protective layer on the surface is activated at 80° C. until the polymer is attached to the electrolyte and the positive and negative electrode surfaces in a gel state.

[0027] (6) Battery performance evaluation: The all-solid-state lithium symmetric battery was subjected to constant potential electrochemical impedance spectroscopy at 25°C with a frequency ranging from 0.1 Hz to 2 MHz. Figure 1 As shown, the interface impedance is about 155ohm / cm 2 ;like Figure 2 As shown, the symmetrical battery is at 0.2 mA / cm 2 The current density can be stably cycled for 400 hours.

[0028] Example 2

[0029] The preparation steps of this embodiment are basically the same as those of Example 1, except that in step 3, a certain amount of polyacrylonitrile (PAN) matrix is ​​completely dissolved in an appropriate amount of N,N-dimethylformamide (DMF) solvent to prepare a 10% polyacrylonitrile solution, and after obtaining a light yellow transparent solution, LATP powder is weighed and added to the above solution to prepare an electrospinning solution with a mass fraction of 0%.

[0030] Example 3

[0031] The preparation steps of this embodiment are basically the same as those of Example 1, except that in step 3, a certain amount of polyacrylonitrile (PAN) matrix is ​​completely dissolved in an appropriate amount of N,N-dimethylformamide (DMF) solvent to prepare a 10% polyacrylonitrile solution, and after obtaining a light yellow transparent solution, LATP powder is weighed and added to the above solution to prepare an electrospinning solution with a mass fraction of 5%.

[0032] Example 4

[0033] The preparation steps of this embodiment are basically the same as those of Example 1, except that in step 3, a certain amount of polyacrylonitrile (PAN) matrix is ​​completely dissolved in an appropriate amount of N,N-dimethylformamide (DMF) solvent to prepare a 10% polyacrylonitrile solution, and after obtaining a light yellow transparent solution, LATP powder is weighed and added to the above solution to prepare an electrospinning solution with a mass fraction of 10%.

[0034] Comparative Example 1

[0035] LATP was prepared according to the method of step 1 of Example 1, and the all-solid-state battery was assembled according to step 5 of Example 1, except that the PVDF-HFP|PAN membrane was not added.

[0036] The present invention and its implementation methods are described above, and such description is not restrictive, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by it, and does not deviate from the purpose of the invention, and does not creatively design a structure and implementation method similar to the technical solution, they should all fall within the protection scope of the present invention.

Claims

1. A lithium aluminum titanium phosphate solid electrolyte polymer interface modification and preparation method thereof, characterized in that: The steps include: S1, taking 4-12 parts by weight of LITFSI, 6-18 parts by weight of PVDF-HFP, and 10-20 mL of dimethyl sulfoxide (DMSO), mixing them, and vigorously stirring at 60° C. to obtain a PVDF-HFP-based polymer mixed solution; S2. A certain amount of polyacrylonitrile (PAN) matrix is ​​completely dissolved in an appropriate amount of N,N-dimethylformamide (DMF) solvent to prepare a 10% polyacrylonitrile solution. After obtaining a light yellow transparent solution, LATP powder is weighed and added to the above solution to prepare electrospinning solutions with mass fractions of 0%, 5%, 10% and 20% in sequence; S3, preparing PAN@LATP composite membrane by electrospinning the spinning solutions of different concentrations obtained in S2; S4, coating the PVDF-HFP-based polymer mixture described in S1 on the composite membrane described in S3 by pressure coating, and vacuum drying to obtain a PVDF-HFP|PAN@LATP membrane; S5, placing the PVDF-HFP|PAN@LATP membrane cut pieces described in S4 on both sides of the LATP electrolyte to assemble into an all-solid-state battery. Activate the all-solid-state battery with a protective layer on the surface at 40-80° C. until the polymer is attached to the electrolyte and the positive and negative electrode surfaces in a gel state.

2. The preparation method according to claim 1, characterized in that: In step S1, the mass ratio of PVDF-HFP to LITFSI is 3:2, and the concentration of LITFSI is 1-5M.

3. The preparation method according to claim 1, characterized in that: In step S2, the LATP powder is synthesized by a hydrothermal method, and the particle size is between 500-600 nm.

4. The preparation method according to claim 1, characterized in that: In step S3, the spinning solution is magnetically stirred at 30-60°C for 10-24h, and the electrospinning speed and time are set to 0.6mL h- 1 and 7 hours.

5. The preparation method according to claim 1, characterized in that: In step S4, the drying temperature is 30-60°C and the drying time is 6-12 hours.

6. Application of the polymer interface modified inorganic solid electrolyte obtained by the preparation method according to any one of claims 1 to 5 in a solid-state lithium battery, characterized in that: The polymer interface modified inorganic solid electrolyte replaces the electrolyte and the separator, lithium metal is used as the negative electrode, and a button battery is assembled.

Images