Preparation method of a partially fluorinated solid-state electrolyte and lithium ion battery
By preparing solid electrolytes through partial fluorination, the problems of low polymerization degree and poor mechanical properties of fluorinated electrolytes in existing lithium-ion batteries are solved, and high ionic conductivity and excellent electrochemical performance are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PEKING UNIV
- Filing Date
- 2023-08-02
- Publication Date
- 2026-05-29
AI Technical Summary
The low degree of polymerization, poor mechanical properties, and low ionic conductivity of fluorinated electrolytes in existing lithium-ion batteries result in poor electrochemical performance.
A partially fluorinated solid electrolyte was prepared by mixing polymerizable acrylate monomers and nitrile compounds, using nonwoven fabric as a matrix, and performing in-situ polymerization under ultraviolet light.
It improves the stability and ionic conductivity of solid electrolytes, enhances mechanical properties, reduces safety hazards, and optimizes electrochemical performance.
Smart Images
Figure CN116979136B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrode material technology, and to a method for preparing a solid electrolyte, specifically a method for preparing a partially fluorinated solid electrolyte and a lithium-ion battery. Background Technology
[0002] Lithium-ion batteries, as the most widely used product in electrochemical energy storage, possess numerous advantages such as high energy density, long cycle life, and a wide operating temperature range, leading to their rapid development over the past few decades. Currently, commonly used lithium-ion batteries generally employ organic liquids as electrolytes. While liquid electrolytes have high ionic conductivity, their volatility and flammability pose safety concerns, hindering their rapid development. Therefore, using solid-state electrolytes to replace liquid electrolytes has become the future development trend of the lithium-ion battery industry.
[0003] Polymer electrolytes are a widely studied type of solid-state electrolyte due to their excellent processability and flexibility. In polymer solid-state electrolytes, fluorinated polymers can form a stable solid electrolyte interphase (SEI) film through the introduction of fluorine atoms, thereby significantly reducing the interfacial impedance and increasing cycle stability. However, the large steric hindrance of fluorinated polymerizable monomers makes in-situ polymerization difficult, ultimately resulting in a low degree of polymerization in the obtained polymer. Therefore, it is essential to develop fluorinated solid-state electrolytes with high polymerization degree and capable of forming a stable SEI interface, and it is also crucial to use these electrolytes to prepare solid-state batteries with excellent charge-discharge performance and safety. Summary of the Invention
[0004] One object of the present invention is to provide a method for preparing a partially fluorinated solid electrolyte to overcome the shortcomings of existing fluorinated electrolytes, such as low degree of polymerization, poor mechanical properties, or low ionic conductivity.
[0005] Another objective of this invention is to provide a lithium-ion battery assembled with a partially fluorinated solid electrolyte, overcoming the shortcomings of existing solid-state batteries assembled with solid electrolytes prepared from fluorinated polymers, which exhibit poor electrochemical performance.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] This invention provides a method for preparing a partially fluorinated solid electrolyte, the method comprising the following steps performed sequentially:
[0008] S1. A polymerizable acrylate monomer composition, a nitrile compound, a lithium salt and a photoinitiator are mixed evenly to prepare a polymerization precursor solution;
[0009] S2. Impregnate the nonwoven fabric in the polymerization precursor solution to obtain the impregnated matrix;
[0010] S3. The impregnated matrix is polymerized in situ under ultraviolet light to obtain a partially fluorinated solid electrolyte;
[0011] In step S1, the polymerizable acrylate monomer composition includes a polymerizable fluorinated acrylate monomer and a polymerizable non-fluorinated acrylate monomer. The polymerizable fluorinated acrylate monomer is a monofunctional polymerizable fluorinated acrylate monomer, and the polymerizable non-fluorinated acrylate monomer includes at least one difunctional polymerizable non-fluorinated acrylate monomer and one monofunctional polymerizable non-fluorinated acrylate monomer.
[0012] As a first limitation on the above preparation method, in step S1, the difunctional polymerizable non-fluorinated acrylate monomer is also referred to as a difunctional polymerizable acrylate monomer in this invention; the monofunctional polymerizable fluorinated acrylate monomer and the monofunctional polymerizable non-fluorinated acrylate monomer are collectively referred to as monofunctional polymerizable acrylate monomers in this invention; the mass of the difunctional polymerizable acrylate monomer is not less than 5 wt% of the mass of the monofunctional polymerizable acrylate monomer;
[0013] In this invention, the monofunctional polymerizable acrylate monomer refers to a polymerizable acrylate monomer containing one carbon-carbon double bond in its monomer molecule; the difunctional polymerizable acrylate monomer refers to a polymerizable acrylate monomer containing two carbon-carbon double bonds in its monomer molecule.
[0014] As a second limitation on the above preparation method, in step S1, the nitrile compound includes succinic anionyl or glutaronitrile; the lithium salt is one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoroborate oxalate, lithium dioxalate borate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, or lithium perchlorate; the photoinitiator includes benzoyl dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone.
[0015] As a third limitation on the above preparation method, in step S2, the nonwoven fabric is at least one of fiber membrane, meltblown fabric or nonwoven membrane.
[0016] As a fourth limitation on the above preparation method, the components in step S1 are mixed according to the following weights:
[0017]
[0018] The polymerizable fluorinated acrylate monomer accounts for 30-70% of the mass of the polymerizable acrylate monomer composition.
[0019] As a further limitation of the above preparation method, in step S3, the wavelength of the ultraviolet light is 350-400 nm.
[0020] As a further limitation on the above preparation method, in step S3, the partially fluorinated solid electrolyte is in the form of a thin film with a thickness of 10 to 200 μm.
[0021] The present invention also provides a lithium-ion battery, wherein the electrolyte of the lithium-ion battery is prepared by the above-described method for preparing a partially fluorinated solid electrolyte.
[0022] By adopting the above technical solution, the technical progress achieved by this invention compared with the prior art is as follows:
[0023] ①Based on the shortcomings of existing fluorinated electrolytes, such as low polymerization degree, poor mechanical properties and low ionic conductivity, this invention proposes a partial fluorination strategy and provides a method for preparing a partially fluorinated acrylate polymer solid electrolyte. The solid electrolyte prepared by this method has reliable stability, is less affected by factors such as water and oxygen, and has excellent mechanical properties and high ionic conductivity.
[0024] ② In the preparation method of the partially fluorinated solid electrolyte provided by the present invention, the degree of polymerization of the polymer obtained after mixing the polymerizable acrylate monomers can be adjusted by changing the ratio of monofunctional polymerizable acrylate monomers and difunctional polymerizable acrylate monomers, and the ratio of polymerizable fluorinated acrylate monomers in the polymerizable acrylate monomer composition, thereby further controlling the mechanical properties and ionic conductivity of the final solid electrolyte.
[0025] ③ In the preparation process of the partially fluorinated solid electrolyte provided by the present invention, the present invention also found that the mass of the difunctional polymerizable acrylate monomer shall not be less than 5 wt% of the mass of the monofunctional polymerizable acrylate monomer, otherwise the resulting polymerization precursor liquid is not easy to form a film.
[0026] ④ In the method for preparing partially fluorinated solid electrolyte provided by the present invention, nitrile compounds are introduced as ionic conductivity additives, which have a certain promoting effect on improving the ionic conductivity of the obtained solid electrolyte; non-woven fabric is used as the matrix, which is not only inexpensive and readily available, but also improves the mechanical properties of the solid electrolyte film.
[0027] ⑤ Compared with existing lithium-ion batteries, lithium-ion batteries assembled using the partially fluorinated solid electrolyte prepared by this invention have fewer safety hazards and better electrochemical performance. Among them, fewer safety hazards are reflected in the fact that the solid electrolyte selected by this battery is more stable and less prone to combustion or explosion. The better electrochemical performance is reflected in the fact that a lithium-ion battery protected by this invention exhibits a discharge specific capacity of 141.2 mAh / g at a 1C current density and still maintains a discharge specific capacity of 119.6 mAh / g after 750 cycles.
[0028] The present invention provides a method for preparing a partially fluorinated solid electrolyte, which can be used to prepare a solid electrolyte and further applied to the preparation of lithium-ion batteries. Attached Figure Description
[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0030] Figure 1 The structural formula of TFEA-EA in Embodiment 1 of the present invention;
[0031] Figure 2 The structure of DECS-EA in Embodiment 1 of the present invention is shown below;
[0032] Figure 3 The structural formula of polyethylene glycol diacrylate in Example 1 of this invention;
[0033] Figure 4 This is a scanning electron microscope image of part of the fluorinated solid electrolyte I in Example 1 of the present invention;
[0034] Figure 5 The results of gel permeation chromatography for three solid electrolytes with different degrees of fluorination in Example 1 of this invention are shown below. Figure 5 a represents the gel permeation chromatography results of the non-fluorinated solid electrolyte and partially fluorinated solid electrolyte I. Figure 5 b represents the gel permeation chromatography results of the perfluorinated solid electrolyte;
[0035] Figure 6 This is a graph showing the ionic conductivity of three solid electrolytes with different degrees of fluorination as a function of temperature in Example 1 of the present invention.
[0036] Figure 7 For the lithium-lithium symmetric battery I, lithium-lithium symmetric battery pair I, and lithium-lithium symmetric battery pair II in Example 8 of the present invention, at 0.1 mA / cm 2 Test results of lithium-ion insertion and extraction experiments at current densities;
[0037] Figure 8 This is a battery cycle performance diagram of lithium-ion battery I in Example 8 of the present invention at a current density of 1C. Detailed Implementation
[0038] The present invention will be further described in detail below through specific embodiments. It should be understood that the described embodiments are preferred examples of the present invention and are only used to explain the present invention and do not limit the present invention.
[0039] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.
[0040] Example 1: A method for preparing a partially fluorinated solid electrolyte
[0041] (I) This embodiment is a method for preparing a partially fluorinated solid electrolyte, which includes the following steps performed sequentially:
[0042] S1. Mix 2,2,2-trifluoroethyl acrylate (TFEA-EA), ethoxyethyl acrylate (DECS-EA), polyethylene glycol diacrylate (PEGDA), nitrile compounds, lithium salt and photoinitiator according to the proportions shown in Table 1, place on a shaker and shake for 5 min, then place in an ultrasonic dispersion device and disperse and sonicate for 20 min to finally obtain a uniformly mixed polymerization precursor liquid, which is denoted as polymerization precursor liquid I;
[0043] S2. [The area is] 10 × 10 cm 2 A 120μm thick meltblown fabric was impregnated into a 500ml screw-top bottle containing 200mL of polymerization precursor solution I and soaked for 3h to obtain the impregnated matrix, which is denoted as impregnated matrix I.
[0044] S3. The impregnated matrix I is taken out from the polymerization precursor solution I and placed under ultraviolet light with a wavelength of 365nm for polymerization for 10min to obtain a partially fluorinated solid electrolyte, which is denoted as partially fluorinated solid electrolyte I.
[0045] In step S1, TFEA-EA is a monofunctional polymerizable fluorinated acrylate monomer with the following structural formula: Figure 1 As shown; DECS-EA is a monofunctional polymerizable non-fluorinated acrylate monomer, and its structural formula is as follows. Figure 2 As shown; PEGDA is a bifunctional polymerizable non-fluorinated acrylate monomer, and its structural formula is as follows. Figure 3 As shown, n takes the form of a positive integer from 3 to 6.
[0046] Table 1. Raw material ratio table for polymerization precursor solution I
[0047]
[0048] As shown in Table 1, the mass ratio of the difunctional polymerizable acrylate monomer (PEGDA) to the monofunctional polymerizable acrylate monomers (TFEA-EA and DECS-EA) is 5.3:100; the mass percentage of the polymerizable fluorinated acrylate monomer in the polymerizable acrylate monomer composition is 47.5%.
[0049] (II) This embodiment also characterizes the thickness and microstructure of the partially fluorinated solid electrolyte I, and measures the average molar mass and ionic conductivity of the partially fluorinated solid electrolyte I, as follows:
[0050] (1) Thickness of partially fluorinated solid electrolyte I
[0051] The thickness of the partially fluorinated solid electrolyte I was measured to be 200 μm.
[0052] (2) Microstructure of partially fluorinated solid electrolyte I
[0053] In this embodiment, the surface structure of partially fluorinated solid electrolyte I was characterized using scanning electron microscopy (SEM). The SEM image of partially fluorinated solid electrolyte I is shown below. Figure 4 As shown.
[0054] Depend on Figure 4 It can be seen that the partially fluorinated solid electrolyte I retains the cross-linked network structure of meltblown fabric while also having a relatively flat polymer surface. This structure ensures the stability of the mechanical properties and mechanical strength of the solid electrolyte, while the relatively flexible and flat surface can further enhance its interfacial properties.
[0055] (3) Preparation of the comparative example
[0056] To explore the effect of the mass ratio of polymerizable fluorinated acrylate monomers in the polymerizable acrylate monomer composition on the overall polymerization degree and ionic conductivity of the solid electrolyte, this embodiment prepared two sets of comparative examples based on a fluorine-free strategy and a perfluorinated strategy, as detailed below.
[0057] Comparative Example 1: Based on the preparation method of Example 1, only TFEA-EA was not added to the raw material ratio table of polymerization precursor liquid I, and the mass ratio of DECS-EA was adjusted from 15% to 30% to ensure that the mass ratio of the polymerizable acrylate monomer composition in polymerization precursor liquid I is 31.6%. The amount of other raw materials and the preparation process parameters remained unchanged. The obtained solid electrolyte was denoted as non-fluorinated solid electrolyte.
[0058] Comparative Example 2: Based on the preparation method of Example 1, only the mass percentage of DECS-EA in the raw material ratio table of polymerization precursor liquid I was added to the mass percentage of TFEA-EA, that is, DECS-EA was not added, and the mass percentage of TFEA-EA was adjusted from 15% to 30%. The amount of other raw materials and the preparation process parameters remained unchanged. The solid electrolyte obtained was denoted as perfluorinated solid electrolyte.
[0059] (3) Determination of the average molar mass of the three solid electrolytes
[0060] The partially fluorinated solid electrolyte I prepared in Example 1, the non-fluorinated solid electrolyte prepared in Comparative Example 1, and the perfluorinated solid electrolyte prepared in Comparative Example 2 were subjected to gel permeation chromatography experiments. The degree of polymerization of the polymer in the reaction system was measured by measuring the average molar mass of the system. The test results are as follows: Figure 5 As shown.
[0061] Depend on Figure 5 It is known that the average molar mass of the perfluorinated solid electrolyte is only 23.8 kg / mol, which may be due to the excessive introduction of fluorine atoms, leading to a significant decrease in the degree of polymerization. The partially fluorinated solid electrolyte I and the non-fluorinated solid electrolyte obtained based on partial fluorination and non-fluorination strategies achieve higher molar masses of approximately 74.2 kg / mol and 78.6 kg / mol, respectively. Higher molar masses imply a higher degree of polymerization and more desirable mechanical properties, providing a foundation for stable electrochemical performance.
[0062] (4) Determination of ionic conductivity of three solid electrolytes
[0063] To determine the ionic conductivity of the partially fluorinated solid electrolyte I prepared in Example 1, the non-fluorinated solid electrolyte prepared in Comparative Example 1, and the perfluorinated solid electrolyte prepared in Comparative Example 2, the three solid electrolytes were first assembled into batteries. Assembly was performed in a glove box according to the sequence of negative electrode shell-spring sheet-gasket-solid electrolyte-gasket-positive electrode shell, followed by button cell encapsulation using a pressure-controlled manual encapsulation machine. After encapsulation, the ionic conductivity was tested using AC impedance spectroscopy, and the test results are shown below. Figure 6 As shown.
[0064] Depend on Figure 6 It can be seen that the ionic conductivity of the non-fluorinated solid electrolyte at room temperature is 0.5 mS / cm, which is much lower than that of the partially fluorinated solid electrolyte I (1.0 mS / cm) and the perfluorinated solid electrolyte (1.1 mS / cm). The high ionic conductivity of the perfluorinated solid electrolyte is partly due to the low degree of polymerization of the polymer and the high content of oligomers.
[0065] In summary, tests on the average molar mass and ionic conductivity of solid electrolytes prepared under non-fluorinated, perfluorinated, and partially fluorinated strategies show that in polymerizable acrylate monomer compositions, if all monofunctional acrylate monomers are used as... Figure 1 The fluorinated acrylate monomers shown lead to a lower degree of polymerization and poorer mechanical properties; if all monofunctional acrylate monomers are used, similar to... Figure 2 The non-fluorinated acrylate monomers shown present a risk of difficulty in forming a stable solid electrolyte interphase (SEI) film after subsequent battery assembly, which can lead to poor electrochemical performance. A partial fluorination strategy can balance the relationship between mechanical and electrochemical performance.
[0066] Preparation methods of partially fluorinated solid electrolytes in Examples 2-7
[0067] Examples 2 to 7 are methods for preparing partially fluorinated solid electrolytes. The partially fluorinated solid electrolytes obtained are labeled as partially fluorinated solid electrolyte II to partially fluorinated solid electrolyte VIII. Their preparation methods are basically the same as those in Example 1, except that the raw materials, dosages and process parameters are different. For details, please refer to Table 2.
[0068] Table 2. Summary of Control Parameters for Examples 2-7
[0069]
[0070] During the experiments in Examples 2 to 7, it was found that the mass of the difunctional polymerizable fluorinated acrylate monomer must not be less than 5 wt% of the mass of the monofunctional polymerizable fluorinated acrylate monomer, otherwise it will be difficult to form a film.
[0071] By measuring the average molar mass and ionic conductivity of partially fluorinated solid electrolytes II to VIII, it was found that partially fluorinated solid electrolytes II to VIII have good polymerization degree and ionic conductivity.
[0072] Example 8: Application of partially fluorinated solid electrolytes in the preparation of lithium-ion batteries
[0073] Given the excellent electrochemical and mechanical properties of fluorinated solid electrolytes, the partially fluorinated solid electrolytes prepared in Examples 1-7 can be used to assemble lithium-ion batteries. In this example, only the partially fluorinated solid electrolyte I prepared in Example 1 was used to assemble a lithium-ion battery, and its electrochemical performance was further investigated.
[0074] The specific method is as follows:
[0075] (1) Electrochemical performance of lithium-lithium symmetric batteries assembled with solid electrolytes prepared under different fluorination strategies
[0076] Using the partially fluorinated solid electrolyte I prepared in Example 1, the non-fluorinated solid electrolyte prepared in Comparative Example 1, and the perfluorinated solid electrolyte prepared in Comparative Example 2 as solid electrolytes, coin cells were assembled. The assembly process was as follows: assembling was carried out in a glove box according to the sequence of negative electrode shell-lithium sheet-solid electrolyte-lithium sheet-gasket-spring sheet-positive electrode shell, followed by coin cell encapsulation using a pressure-controlled manual encapsulation machine to assemble lithium-lithium symmetric batteries. The lithium-lithium symmetric batteries assembled using the partially fluorinated solid electrolyte I, the non-fluorinated solid electrolyte prepared in Comparative Example 1, and the perfluorinated solid electrolyte prepared in Comparative Example 2 were respectively designated as lithium-lithium symmetric battery I, lithium-lithium symmetric battery II, and lithium-lithium symmetric battery III.
[0077] The three types of lithium-ion symmetric batteries assembled above were subjected to lithium-ion insertion and extraction experiments, and the measured current density was 0.1 mA / cm². 2 The test results are as follows Figure 7 As shown.
[0078] Depend on Figure 7 It can be seen that the lithium-lithium symmetric battery II is relatively unstable in cycling, and a short circuit occurs after about 50 hours of cycling. The reason may be that the non-fluorinated solid electrolyte does not form a stable SEI film due to the lack of fluorine atoms, which further leads to the unstable cycling of the assembled battery. After 50 hours, the voltage of the lithium-lithium symmetric battery III gradually increased from 50mV to 5V. The reason is that the polymer in the perfluorinated solid electrolyte has a low degree of polymerization, resulting in an unstable interface. In contrast, the lithium-lithium symmetric battery I can cycle stably for more than 800 hours, showing excellent electrochemical stability.
[0079] (2) Electrochemical performance of lithium metal full batteries equipped with partially fluorinated solid electrolytes
[0080] A 12mm diameter lithium sheet was used as the negative electrode of the coin cell, lithium iron phosphate paste (LFP) was used as the positive electrode, and the partially fluorinated solid electrolyte I obtained in Example 1 was used as the solid electrolyte. The assembled coin cell was designated as lithium metal full cell I, and its electrochemical performance was tested. The test results are as follows: Figure 8 As shown.
[0081] like Figure 8 It can be seen that at a current density of 1C, the lithium metal full battery I exhibits a discharge specific capacity of 141.2 mAh / g, and still maintains a discharge specific capacity of 119.6 mAh / g after 750 cycles. This shows that the lithium metal full battery I exhibits excellent electrochemical performance.
[0082] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.
Claims
1. A method for preparing a partially fluorinated solid electrolyte, characterized in that, The preparation method includes the following steps performed sequentially: S1. A polymerizable acrylate monomer composition, a nitrile compound, a lithium salt and a photoinitiator are mixed evenly to prepare a polymerization precursor solution; S2. Impregnate the nonwoven fabric in the polymerization precursor solution to obtain the impregnated matrix; S3. The impregnated matrix is polymerized under ultraviolet light to obtain a partially fluorinated solid electrolyte; In step S1, the polymerizable acrylate monomer composition includes a polymerizable fluorinated acrylate monomer and a polymerizable non-fluorinated acrylate monomer. The polymerizable fluorinated acrylate monomer is a monofunctional polymerizable fluorinated acrylate monomer, and the polymerizable non-fluorinated acrylate monomer includes at least one difunctional polymerizable non-fluorinated acrylate monomer and one monofunctional polymerizable non-fluorinated acrylate monomer. In step S1, the mass of the difunctional polymerizable non-fluorinated acrylate monomer is denoted as A, and the total mass of the monofunctional polymerizable fluorinated acrylate monomer and the monofunctional polymerizable non-fluorinated acrylate monomer is denoted as B, wherein A is not less than 5 wt% of B. The polymerizable fluorinated acrylate monomer accounts for 30-70% of the mass of the polymerizable acrylate monomer composition.
2. The method for preparing a partially fluorinated solid electrolyte according to claim 1, characterized in that, In step S1, The nitrile compounds include butadionitrile or glutaronitrile; The lithium salt is one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoroborate oxalate, lithium dioxalate borate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, or lithium perchlorate. The photoinitiator includes benzoyl dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or 2-methyl-1-(4-methylthiophenyl)-2-morpholin-1-propanone.
3. The method for preparing a partially fluorinated solid electrolyte according to claim 1, characterized in that, In step S2, the nonwoven fabric is at least one of fiber membrane, meltblown fabric, or nonwoven membrane.
4. A method for preparing a partially fluorinated solid electrolyte according to any one of claims 1 to 3, characterized in that, The components in step S1 are mixed according to the following weights: 。 5. The method for preparing a partially fluorinated solid electrolyte according to claim 4, characterized in that, In step S3, the wavelength of the ultraviolet light is 350–400 nm.
6. The method for preparing a partially fluorinated solid electrolyte according to claim 4, characterized in that, The partially fluorinated solid electrolyte mentioned in step S3 is in the form of a thin film with a thickness of 10–200 μm.
7. A lithium-ion battery, characterized in that, The electrolyte of the lithium-ion battery is prepared by the method for preparing a partially fluorinated solid electrolyte according to any one of claims 1 to 5.