Solid electrolyte based on 3D printing, preparation method and lithium battery

Abstract

The invention belongs to the technical field of solid electrolyte preparation, and particularly relates to a solid electrolyte based on 3D printing, a preparation method and a lithium battery, and the preparation method comprises the following steps: uniformly mixing LLZTO and PVDF powder in a mortar; the preparation method comprises the following steps: adding lithium salt into N, N-dimethylformamide, mixing to form a uniform solution, then adding the obtained mixture into the lithium salt mixed solution, and continuously stirring until the mixture is uniform to obtain printable slurry; and injecting the printable slurry into a needle tube, printing a designed shape through a direct writing type 3D printer, and drying to remove the organic solvent to obtain the PVDF-LLZTO composite solid electrolyte membrane. According to the technical scheme provided by the invention, the ionic conductivity of the electrolyte can be remarkably improved, meanwhile, the electrochemical window of the electrolyte can be improved, and the assembled all-solid-state battery shows excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for producing solid electrolytes based on 3D printing. Background Art

[0002] The rapid development of industries such as portable mobile devices and electric vehicles has led to an increasing demand for energy storage devices. In particular, lithium-ion batteries with high energy density and operating voltage dominate the energy storage device market.

[0003] Traditional lithium-ion batteries mainly use organic liquid electrolytes such as ethers and esters, which have problems such as low electrochemical stability, serious interface side reactions, flammability, explosion, and leakage. These problems can be solved by using solid electrolytes with high thermal stability instead of organic liquid electrolytes. At the same time, solid electrolytes allow the direct use of high theoretical specific capacity (3860mAh g -1 )’s lithium metal replaces the graphite negative electrode to assemble a lithium metal battery, further improving the energy density of the battery without worrying about the problem of lithium dendrites.

[0004] Specifically, the composite solid electrolyte is composed of a polymer matrix and an inorganic filler. The introduction of the inorganic filler can improve the ionic conductivity and mechanical strength of the polymer matrix. The decorative groups on the inorganic filler can also change the local structure and increase the lithium ion concentration and mobility. Therefore, it is very important to choose a suitable filler. So far, solid electrolytes can be divided into three categories: inorganic ceramic electrolytes, organic polymer electrolytes and composite electrolytes. Among them, inorganic ceramic electrolytes have higher ionic conductivity (10 -3 -10 -2 S cm -1 ), wide electrochemical window, high mechanical strength, and poor interface contact. Organic polymer electrolytes are composed of polymer matrices doped with lithium salts, showing good processability, flexibility and safety, and good interface contact with electrodes, but their ionic conductivity is low (<10 -4 S cm -1 ), and its thermal stability and electrochemical stability are poor. The composite electrolyte is composed of an organic polymer electrolyte matrix and a ceramic filler. It inherits the good ionic conductivity and high mechanical properties of the ceramic electrolyte, and also has good interface contact with the electrode, which greatly improves the electrochemical performance of the solid-state battery.

[0005] At present, the methods for preparing composite solid electrolytes are mainly coating and mold forming, which have poor flexibility and cannot achieve flexible control of the shape and thickness of the electrolyte. Summary of the invention

[0006] Based on this, it is necessary to provide a method for preparing PVDF-LLZTO composite solid electrolyte based on 3D printing, which can achieve flexible control of the shape and thickness of the electrolyte, while ensuring or even improving the ionic conductivity and mechanical properties.

[0007] The present invention adopts the following technical solution:

[0008] The present invention provides a method for preparing a PEO-LLZTO composite solid electrolyte based on 3D printing, comprising the following steps:

[0009] Add lithium salt and PVDF in a molar ratio of 1: (10-25) to N,N-dimethylformamide, stir evenly to obtain a mixed solution; add LLZTO filler to the mixed solution, stir evenly to obtain a slurry; transfer the slurry into a syringe, 3D print it onto a substrate to form a blank of a preset shape, and vacuum dry it to obtain the product.

[0010] In some embodiments, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide) salt, and lithium perchlorate.

[0011] In some embodiments, the molar ratio of lithium salt to PEO is preferably 1:18.

[0012] In some embodiments, the LLZTO filler has a particle size ranging from 300 nm to 1 μm.

[0013] In some of the embodiments, the amount of LLZTO filler is 10-30 wt % of the total amount of PVDF and LiTFSI.

[0014] In some embodiments, the process parameters of 3D printing are: 0.1-3 MPa. The process parameters of 3D printing are preferably 0.1-2 MPa.

[0015] In some embodiments, the vacuum drying temperature is 55-65°C.

[0016] In some embodiments, the stirring temperature is 50-60°C.

[0017] The PVDF-LLZTO composite solid electrolyte prepared by the above method.

[0018] The present invention can also provide a lithium battery, comprising the PVDF-LLZTO composite solid electrolyte prepared by the above method.

[0019] The beneficial effects of the present invention are:

[0020] Compared with the prior art, the present invention proposes and realizes for the first time the preparation of PVDF-LLZTO composite solid electrolyte using 3D printing, which can realize the customization of the shape and thickness of the solid electrolyte, while ensuring or even improving the ionic conductivity and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Optical photographs of PVDF-LLZTO solid electrolytes of different shapes prepared in Example 1.

[0022] Figure 2 The impedance spectrum test diagram of the composite PVDF-LLZTO solid electrolyte prepared in Example 3 and Comparative Example 1.

[0023] Figure 3 This is a scanning electron microscope image of the composite PVDF-LLZTO solid electrolyte prepared in Example 2.

[0024] Figure 4 3 and 1 are thermogravimetric curves of the composite PVDF-LLZTO solid electrolyte prepared in Example 3 and Comparative Example 1.

[0025] Figure 5 It is the linear voltammetric scanning curve of the composite PVDF-LLZTO solid electrolyte prepared in Example 3 and Comparative Example 1.

[0026] Figure 6 The charge and discharge curves of the lithium battery prepared in Example 3 at different cycles at 0.4C. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand the present invention more clearly.

[0028] The following embodiments are only used to illustrate the present invention, but are not limited to the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work belong to the protection scope of the present invention.

[0029] In the examples of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the examples of the present invention, unless otherwise specified, the technical means used are conventional means well known to those skilled in the art.

[0030] This application is aimed at the method steps of composite solid electrolyte product testing:

[0031] Ionic conductivity is measured by assembling stainless steel / electrolyte / stainless steel mold cells using a corrtest electrochemical workstation with an AC impedance frequency range of 1MHz to 1Hz and an amplitude of 10mV. The calculation of ionic conductivity (σ) is based on the following equation: Where L is the thickness of the electrolyte membrane, R is the resistance of the electrolyte, and A is the contact area between the electrolyte and the stainless steel electrode (10mm).

[0032] Lithium cobalt oxide (LiCoO 2 ) positive electrode, the solid electrolyte printed by the present invention and a lithium sheet were used to assemble a CR2032 solid-state lithium battery. Using LAND CT3001A, a charge and discharge test at a rate of 0.4C was performed at room temperature within a voltage range of 2.5-4.2V.

[0033] Lithium sheets were used as positive and negative electrodes, and the solid electrolyte printed by the present invention was used to assemble a CR2032 solid-state lithium symmetric battery. LAND CT3001A was used to conduct the test at 0.1 mA·cm -2 The constant current charge and discharge test was carried out at 25°C with a voltage and current density of 1.

[0034] Example 1

[0035] This embodiment provides a method for preparing a composite solid electrolyte, comprising the following steps:

[0036] S1. Weigh 0.181 g of lithium bis(trifluoromethanesulfonyl)imide LiTFSI and 0.5 g of polyvinylidene fluoride PVDF, add them into 10 mL of N,N-dimethylformamide, and stir them magnetically at 60° C. for 3 h to obtain a mixed solution.

[0037] S2. Weigh 0.051 g of LLZTO and add it to the mixed solution. Continue magnetic stirring at 60° C. overnight to obtain a slurry.

[0038] S3. Add the slurry obtained in step S2 into a syringe, set the pressure to 0.15 MPa, print it on a glass plate according to the set three-dimensional size program, and then place it in a vacuum oven at 80° C. to dry for 24 hours to obtain a composite solid electrolyte.

[0039] Depend on Figure 1 It can be seen from the optical photographs of PVDF-LLZTO solid electrolytes of different shapes that the shape of the solid electrolyte can be customized by using the preparation method of this embodiment.

[0040] Depend on Figure 2 It can be seen that compared with the composite solid electrolyte prepared by the conventional process, the preparation method adopted in this embodiment has higher ion conductivity.

[0041] Example 2

[0042] This example explores the effect of different printed LLZTO contents on the composite solid electrolyte, including the following steps:

[0043] S1. Weigh 1 g of LiTFSI and 3 g of PVDF, add them into 25 mL of N,N-dimethylformamide, and stir them magnetically at 60°C for 1 h to obtain a mixed solution.

[0044] S2. Weigh 0.333 g, 0.75 g, 1 g, and 1.285 g of LLZTO particles respectively and add them to the mixed solution. Continue magnetic stirring for 12 h to obtain a slurry.

[0045] S3. Add the slurry obtained in step S2 into a syringe, print it on a substrate according to a set three-dimensional size program, and then place it in a vacuum oven at 60° C. and dry it for 24 hours to obtain a composite solid electrolyte.

[0046] SEM images of PVDF-LLZTO solid electrolytes with different LLZTO contents are shown in Figure 3 .

[0047] Example 3

[0048] This embodiment provides a method for preparing a composite solid electrolyte, comprising the following steps:

[0049] S1. Weigh 1-1.2 g LiTFSI and 3 g PVDF, add into 30 mL N,N-dimethylformamide, stir magnetically at 60° C. for 1 h to obtain a mixed solution.

[0050] S2. Weigh 0.75 g of LLZTO particles and add them to the mixed solution. Continue magnetic stirring for 12 h to obtain a slurry.

[0051] S3. Add the slurry obtained in step S2 into a syringe, print it on a substrate according to a set three-dimensional size program, and then place it in a vacuum oven at 80° C. to dry for 24 hours to obtain a composite solid electrolyte.

[0052] Figure 6 The figure is the charge and discharge curve of the lithium battery prepared in Example 3 at different cycles at 0.4C. The average specific capacity of the battery is 156 mAh / g, the coulomb efficiency is above 98%, and the capacity retention rate is 97.35%. This shows that the lithium ion battery prepared in this example can maintain high capacity in a long cycle and has good cycle stability.

[0053] Comparative Example 1

[0054] S1. Weigh 1-1.2 g LiTFSI and 3 g PVDF, add into 30 mL N,N-dimethylformamide, stir magnetically at 60° C. for 1 h to obtain a mixed solution.

[0055] S2. Weigh 0.75 g of LLZTO particles and add them to the mixed solution. Continue magnetic stirring for 12 h to obtain a slurry.

[0056] S3. Use a scraper to coat the prepared slurry on a glass dish, and then place it in a vacuum oven at 80° C. to dry for 24 hours to obtain a composite solid electrolyte.

[0057] Experimental Example 1: Thermal stability test of the PVDF-LLZTO composite solid electrolyte used in the present invention

[0058] The composite solid electrolyte membranes prepared in Example 3 and Comparative Example 1 were subjected to thermogravimetric analysis.

[0059] from Figure 4 It can be seen that the composite solid electrolyte prepared in Experimental Example 3 has a higher temperature at which thermal degradation begins than that in Comparative Example 1, indicating that Experimental Example 1 has better thermal stability.

[0060] Experimental Example 2: Performance test of the all-solid-state battery prepared using the PVDF-LLZTO composite solid electrolyte of the present invention.

[0061] An all-solid-state battery was assembled using the composite solid electrolyte membrane prepared in Example 3 and Comparative Example 1, as well as a stainless steel sheet and a lithium sheet, and a linear voltammetric sweep test was performed.

[0062] from Figure 5 It can be seen that the electrochemical window of Experimental Example 3 reaches 4.73 V, while the electrochemical window of Comparative Example 1 is only 4.47 V, which indicates that the electrolyte membrane prepared by this scheme can effectively broaden the electrochemical window.

Claims

1. A method for preparing PVDF-LLZTO composite solid electrolyte based on direct writing 3D printing, characterized in that: The steps include: Add lithium salt and PVDF in a molar ratio of 1:(10-25) into an organic solvent, stir evenly, and obtain a mixed solution; Adding LLZTO inorganic filler into the mixed solution and stirring evenly to obtain slurry; The slurry is transferred into a syringe, 3D printed onto a substrate to form a preset shape, and vacuum dried to obtain the product.

2. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to claim 1, characterized in that: The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide) salt, and lithium perchlorate, and the organic solvent is N,N-dimethylformamide.

3. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to claim 2, characterized in that: The molar ratio of lithium salt to PEO is 1:

18.

4. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to claim 1, characterized in that: The particle size of the LLZTO filler ranges from 300 nm to 5 μm.

5. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to claim 1, characterized in that: The amount of LLZTO filler used is 10-30 wt% of the total amount of PVDF.

6. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to any one of claims 1 to 5, characterized in that: The process parameters of 3D printing are: 1.5~4MPa.

7. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to any one of claims 1 to 5, characterized in that: The vacuum drying temperature is 65-85°C.

8. The method for preparing a PVDF-LLZTO composite solid electrolyte based on 3D printing according to any one of claims 1 to 5, characterized in that: The stirring temperature is 50-60°C.

9. The PVDF-LLZTO composite solid electrolyte prepared by the method according to claim 8.

10. A lithium battery, characterized in that: Includes the PVDF-LLZTO composite solid electrolyte as described in claim 9.

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