A low-skeleton fluorinated gel electrolyte, its preparation method, and a lithium battery thereof

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a low-skeleton-content fluorinated gel electrolyte, its preparation method, and a battery thereof. The low-skeleton-content fluorinated gel electrolyte comprises an organic gelling agent, a lithium salt, and a solvent. The organic gelling agent has a structure according to formula (I), where m is an integer from 12 to 18, and n is an integer from 5 to 10. This organic gelling agent, with an incorporation amount of 0.3 to 3 wt%, can achieve gelation of the liquid electrolyte, resulting in a low-skeleton-content fluorinated gel electrolyte. The fluorinated gel electrolyte of this invention exhibits a high ionic conductivity greater than 15.0 mS / cm at room temperature and excellent lithium dendrite suppression capability, which is beneficial to the long-cycle stability of lithium-ion batteries. (I)

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a low-skeleton fluorinated gel electrolyte, its preparation method, and a lithium battery. Background Technology

[0002] Developing high-energy-density battery technology is crucial for promoting energy structure transformation and upgrading and achieving dual-carbon goals. Gel electrolyte-based lithium metal batteries (LMBS), with their high theoretical capacity of 3860 mAh / g and low electrochemical potential (3.04 V lower than the standard hydrogen electrode (SHE), combined with the good ionic conductivity of liquid electrolytes and the safety of solid electrolytes, are strong contenders for next-generation high-energy-density and safe batteries. However, existing gel electrolytes still cannot overcome the formation and growth of lithium dendrites. Dendrite growth leads to short circuits and thermal runaway, which are key issues affecting battery safety and cycle life. Effectively suppressing dendrite growth in gel electrolytes is a major challenge facing gel electrolyte-based lithium metal batteries.

[0003] It is generally believed in the art that gel electrolytes need to possess high mechanical strength in order to effectively suppress lithium dendrites, thus requiring a high content of polymer backbone. However, the presence of a high backbone content (≥20wt%) reduces the ionic conductivity of the gel electrolyte. In addition, some researchers have designed novel polymer structures and crosslinking agents from a molecular design perspective. Although this can yield gel electrolyte membranes with high macroscopic mechanical strength, their ionic conductivity is relatively low, and the preparation process is complex.

[0004] CN121507085A discloses a wide-temperature-range, high-specific-energy fluorinated gel electrolyte, its preparation method, and its applications. This gel electrolyte comprises a lithium salt, a (meth)acrylate monomer, a fluorinated sulfonate plasticizer, and a crosslinking agent. The molar concentration of lithium salt relative to the total volume of the fluorinated sulfonate plasticizer and (meth)acrylate monomer is 2-5 mol / L, and the volume ratio of (meth)acrylate monomer to fluorinated sulfonate plasticizer is 2-4:8-6. The gel electrolyte of this invention exhibits a room-temperature ionic conductivity exceeding 2 mS / cm and an electrochemical window exceeding 5 V. It also possesses good stability when matched with high-voltage cathodes and with lithium metal and silicon-carbon anodes, demonstrating excellent cycling performance over a wide temperature range (-20~60℃). However, the ionic conductivity of this gel electrolyte is significantly lower than that of liquid electrolytes. Summary of the Invention

[0005] To address the contradiction between ionic conductivity and dendrite suppression in the aforementioned gel electrolytes, this invention, from a supramolecular chemistry perspective, designs an organic gelling factor with self-assembly capabilities and excellent compatibility with lithium metal. This organic gelling factor can form a network through intermolecular and intramolecular interactions at low concentrations, thereby achieving gelation of the liquid electrolyte and obtaining a thermally reversible fluorinated gel electrolyte with low framework content. This gel electrolyte, through its uniform microstructure and the synergistic effect of interfacial chemistry, achieves high ionic conductivity, dendrite suppression, and long cycling performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A fluorinated gel electrolyte with low skeleton content comprises an organic gelling agent, a lithium salt, and a solvent, wherein the organic gelling agent has the structure shown in Formula I;

[0008] (Formula I)

[0009] In Equation I, m is an integer from 12 to 18, and n is an integer from 5 to 10.

[0010] Preferably, in Formula I, m is an integer from 16 to 18, and n is an integer from 8 to 10; more preferably, m is 16 and n is 8.

[0011] Furthermore, based on the total mass of the fluorinated gel electrolyte with the low skeleton content, the content of the organic gelling factor is 0.3~3.0 wt%, preferably 1.0~1.5 wt%, the lithium salt content is 10~20 wt%, and the solvent content is 75~88 wt%. Compared with the skeleton content of conventional gel electrolytes (generally >20 wt%), the organic gelling factor of the present invention serves as the skeleton, resulting in a lower skeleton content in the gel electrolyte, thus achieving a low skeleton content (0.3~3.0 wt%).

[0012] The core of this invention lies in using an organic gelling agent with a specific structure of Formula I as a framework, which enables gelation at low concentrations, thereby achieving high Li +The flux is high, and excellent structural stability is ensured. It is speculated that the mechanism is mainly due to the unique "triblock" structure of the molecule of Formula I. The molecule shown in Formula I consists of three parts: medium-length (C12-C18) alkyl chains and medium-length (C5-C10) perfluoroalkyl chains at both ends of the molecular chain, and a rigid center (benzene ring) connecting the two. (1) The benzene ring at the center of the molecule provides strong π-π stacking, driving the gelling factor to first form a stable and ordered dimer or polymer core in the solution, laying an ordered seed foundation for the subsequent growth of one-dimensional fibers. (2) Starting from the rigid aromatic core, the medium-length (C12-C18) alkyl chains and medium-length (C5-C10) perfluoroalkyl chains at both ends of the molecular chain extend and aggregate. The C12-C18 alkyl chains interact through van der Waals forces; meanwhile, the C5-C10 perfluorinated segments and alkyl chains have polarity differences, and the fluorinated chains themselves have strong fluorine-fluorine interactions. Under the template effect of the aforementioned rigid core, the two jointly drive the gelling factor to self-assemble in the solvent to form a one-dimensional nanofiber structure. The fibers further entangle and connect to form a fiber network, restricting the flow of solvent to form a gel. (3) The thioether group (-S-) and ester group (-COO-) connecting the benzene ring and the end chain not only act as flexible connecting arms, but also contribute dipole-dipole interactions, further stabilizing the fiber network and promoting efficient gelation. This supramolecular chemical action is different from traditional chemical crosslinking. It can achieve gelation with extremely low skeleton content to form a uniform fiber network, which is the key to achieving high ion flux and maintaining high ion conductivity. Moreover, the gel obtained has thermal reversibility. Furthermore, the fluorinated segments and sulfides in the organic gelling agent may partially participate in the formation of the SEI film during battery cycling, inducing the in-situ generation of a stable SEI layer rich in components such as LiF and Li2S, thus achieving in-situ optimization of interface chemistry. The synergistic effect of the physical network regulating ion transport and the chemical composition optimizing the interface, as described above, enables the fluorinated gel electrolyte of this invention to maintain high ionic conductivity while exhibiting excellent lithium dendrite suppression ability and cycling stability.

[0013] The values ​​of m and n in the above structural formula must fall within the specified range. The value of m indicates the length of the alkyl chain. When the alkyl chain is too short (m ≤ 10), the organic gelling agent has good solubility in the solvent, but is insufficient to form fibrous aggregates at room temperature. When the alkyl chain is too long (m > 18), the organic gelling agent has poor solubility in the solvent, and the van der Waals forces between the alkyl chains disrupt its dissolution-precipitation balance in the perfluorinated solvent, causing the gelling agent to precipitate in crystalline form rather than forming a gel network. Similarly, the value of n indicates the length of the perfluorinated chain segment. If the value is too small, the organic gelling agent has good solubility in the solvent and cannot form a gel; if the value is too large, the organic gelling agent has poor solubility and easily precipitates in crystalline form. The range of 5 to 10 can maintain a good dissolution-precipitation balance.

[0014] Further, the organic gelling factor is prepared by the following method: 4-(2-haloethyl)phenylacetic acid, perfluoroC5-C10 alkylethyl thiol, and an acid-binding agent are dissolved in a first solvent, stirred and reacted to obtain a crude intermediate product, which is then washed, dried, and rotary evaporated to obtain an intermediate; the intermediate, C12-C18 alkyl alcohol, catalyst, and dehydrating agent are dissolved in a second solvent, reacted and filtered, and the solids are rotary evaporated to obtain a crude product; the crude product is purified to obtain the organic gelling factor shown in Formula I.

[0015] Furthermore, the molar ratio of the 4-(2-haloethyl)phenylacetic acid, perfluoroC5-C10 alkylethyl thiol, and acid-binding agent is 1:(1~1.2):(1.8~2.5); the 4-(2-haloethyl)phenylacetic acid is selected from at least one of 4-(bromoethyl)phenylacetic acid and 4-(chloroethyl)phenylacetic acid; the perfluoroC5-C10 alkylethyl thiol is selected from 1H, 1H, 2H, 2H-perfluoro-1-heptyl thiol, 1H, 1H, 2H, 2H-perfluoro-1-octyl thiol, 1H, 1H, 2H, 2H-perfluoro-1-nonyl thiol, 1H, 1H, 2H, 2H-perfluoro-1-dec ... The first solvent is an aprotic polar solvent selected from at least one of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC); the reaction conditions are: reaction at 20-40°C for 1-2 hours; the washing method is: dissolving the intermediate crude product in ethyl acetate, washing with dilute hydrochloric acid, then washing with pure water, and collecting the ethyl acetate phase; the drying method is: drying the ethyl acetate phase with MgSO4 (to remove water).

[0016] Furthermore, the molar ratio of the intermediate, C12-C18 alkyl alcohol, catalyst, and dehydrating agent is 1:(1.5~2.0):(0.3~0.5):(1.5~2.5); the catalyst is selected from at least one of 4-dimethylaminopyridine (DMAP) and 4-pyrrolidinylpyridine (PPY); the dehydrating agent is selected from at least one of N,N'-dicyclohexylcarbodiimide (DCC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), and N,N'-diisopropylcarbodiimide (DIC); the second solvent is dichloromethane; the reaction conditions are: reaction at 20~40℃ for 15~24h; the purification treatment is: the crude product is subjected to silica gel column chromatography.

[0017] Taking 4-(bromoethyl)phenylacetic acid, 1H, 1H, 2H, 2H-perfluoro-1-decathiol and 1-hexadecyl alcohol as examples (n=8, m=16), the reaction formulas are as follows:

[0018]

[0019] Furthermore, the lithium salt is a fluorinated lithium salt, specifically selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisfluorosulfonylimide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiOTf), lithium nitrate (LiNO3), and lithium perchlorate (LiClO4).

[0020] Further, the solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), methyl ethyl carbonate (EMC), fluoroethylene carbonate (FEC), dimethyl fluorocarbonate (FDMC), methyl trifluoroethyl carbonate (FEMC), propylene fluorocarbonate (FPC), diethyl fluorocarbonate (FDEC), dimethyl difluorocarbonate (DFDMC), diethylene difluorocarbonate (DFEC), and ethylene trifluorocarbonate (TFEC); preferably at least one of fluoroethylene carbonate (FEC), dimethyl fluorocarbonate (FDMC), methyl trifluoroethyl carbonate (FEMC), propylene fluorocarbonate (FPC), diethyl fluorocarbonate (FDEC), dimethyl difluorocarbonate (DFDMC), diethylene difluorocarbonate (DFEC), and ethylene trifluorocarbonate (TFEC), and preferably all solvents are fluorinated solvents.

[0021] The gel-sol transition temperature of the low-skeleton fluorinated gel electrolyte described in this invention is 50~70℃. This temperature range is suitable for the application requirements of batteries: on the one hand, this temperature is much higher than the conventional storage, transportation and operating temperature of batteries, ensuring that the electrolyte maintains a stable gel state during daily use and eliminating the risk of leakage; on the other hand, this temperature also allows the electrolyte to be converted into a flowing liquid state with only gentle heating during the battery filling process, enabling convenient filling of the battery casing.

[0022] Secondly, the present invention also provides a method for preparing the above-mentioned low-skeleton-content fluorinated gel electrolyte, comprising the following steps:

[0023] (S1) Mix the solvent and lithium salt according to the specified ratio to obtain a liquid electrolyte;

[0024] (S2) Add the organic gelling factor to the liquid electrolyte, heat to dissolve, and then cool to room temperature and let stand to obtain a fluorine-containing gel electrolyte with low skeleton content.

[0025] The above preparation process is illustrated in Figure 1.

[0026] Further, in step (S2), the heating is performed at 70~90℃; the settling time is 10~30min.

[0027] It should be noted that, since the low-skeleton-content fluorinated gel electrolyte of the present invention is thermally reversible, it is prepared in situ in practical applications. That is, the organic gelling agent and liquid electrolyte are first assembled into the lithium battery under heating, and then cooled to room temperature and allowed to stand for in situ gelation to obtain the low-skeleton-content fluorinated gel electrolyte.

[0028] Thirdly, the present invention also provides a lithium battery, the lithium battery comprising a positive electrode, a separator, a negative electrode and the above-mentioned low-skeleton fluorinated gel electrolyte.

[0029] The positive electrode, separator, and negative electrode are all materials well known in the art and are not particularly limited. For example, the positive electrode can be selected from lithium iron phosphate (LiFePO4) positive electrode, lithium iron manganese phosphate (LiFe) positive electrode, etc. 1-x Mn x Lithium vanadium fluorophosphate (LiVPO4F) cathode, lithium iron phosphate (LiFeSO4F) cathode, nickel cobalt manganese (LiNi) cathode 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 O2) ternary cathode, nickel-cobalt-aluminum (LiNi) x Coy Al z The positive electrode can be either O2 (x+y+z=1, usually x≥0.8) or lithium cobalt oxide (LiCoO2). The separator can be any of the following: a polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer separator, a polypropylene / polyethylene (PP / PE) two-layer separator, a polypropylene (PP) separator, a polyethylene (PE) separator, a cellulose-based separator, a glass fiber separator, or a polymer electrolyte separator (solid / semi-solid). The negative electrode can be any of the following: lithium cobalt oxide (LiCoO2) negative electrode, or lithium titanate (Li4Ti5O2). 12 One of the following: negative electrode, carbon-based (graphite / hard carbon) negative electrode, alloy (silicon-based alloy and tin-based alloy) negative electrode, lithium-based composite (lithium-carbon and lithium-metal oxide) negative electrode and lithium metal negative electrode.

[0030] The present invention also provides an organic gelling factor for gel electrolytes, the structural formula of which is shown in Formula I below:

[0031] (Formula I)

[0032] In Equation I, m is an integer from 12 to 18, and n is an integer from 5 to 10.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention provides a novel organic gelling factor that possesses self-assembly capability and excellent compatibility with lithium metal. It can form an interaction network at low concentrations (0.3~3 wt%) to achieve gelation of liquid electrolytes, resulting in a thermally reversible fluorinated gel electrolyte with low framework content. This fluorinated gel electrolyte exhibits ionic conductivity (>15.0 mS / cm at room temperature) and effectively inhibits lithium dendrite nucleation and growth, which is beneficial for the long-cycle stability of the battery.

[0035] 2. The fluorinated gel electrolyte of the present invention is rich in fluorine. The fluorine-containing component can induce interfacial chemistry, promote the formation of LiF-rich solid electrolyte interface, optimize interfacial performance, and further improve the long-cycle stability of the battery, so that the battery retains more than 90% of its capacity after 1000 cycles. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the preparation process of the low-skeleton-content fluorinated gel electrolyte of the present invention.

[0037] Figure 2 To prepare the organogel factor LMOG-1 obtained in Example 1 1 H NMR spectrum.

[0038] Figure 3The gel behavior state diagram of the organic gelling factor LMOG-1 prepared in Example 1.

[0039] Figure 4 The graph shows the changes in storage modulus G' and loss modulus G'' of the gel electrolyte LMOG-1-FGE with the concentration of gelling factor.

[0040] Figure 5 The image shows the SEM image of the fluorinated gel electrolyte LMOG 1-FGE-1.0 prepared in Example 1 after the lithium salt and solvent have been removed.

[0041] Figure 6 The image shows a comparison of the FT-IR spectra of the fluorinated gel electrolyte LMOG 1-FGE-1.0 prepared in Example 1 and LiTFSI.

[0042] Figure 7 The figure shows the chronoamperometry curve of the fluorinated gel electrolyte LMOG 1-FGE-1.0 prepared in Example 1 at a polarization voltage of 10 mV. The inset shows the electrochemical impedance spectroscopy before and after polarization.

[0043] Figure 8 The symmetric cell Li|LMOG 1-FGE|Li assembled with the fluorinated gel electrolyte of Example 1 and the symmetric cell Li|FLE|Li with the liquid electrolyte (FLE) at 2 mA / cm 2 2 mAh / cm 2 The constant current cycling curve.

[0044] Figure 9 The symmetric cell Li|LMOG 1-FGE|Li assembled with the fluorinated gel electrolyte of Example 1 and the symmetric cell Li|FLE|Li with the liquid electrolyte (FLE) at 0.2 mA / cm 2 0.2 mAh / cm 2 The constant current cycling curve.

[0045] Figure 10 SEM images of the lithium metal surface of the symmetric battery Li|LMOG 1-FGE|Li assembled with the fluorinated gel electrolyte of Example 1 after 50 and 100 cycles.

[0046] Figure 11 SEM images of the lithium metal surface of a symmetric battery Li|FLE|Li assembled with a liquid electrolyte after 50 and 100 cycles.

[0047] Figure 12 The cycling curves are shown for the lithium-ion battery Li|FLE|LFP assembled with the liquid electrolyte using the lithium-ion battery Li|LMOG 1-FGE|LFP prepared in Example 1. Detailed Implementation

[0048] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0049] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0050] Preparation of organogel factors

[0051] Preparation Example 1

[0052] Step 1: Add 5 mmol of 4-(bromoethyl)phenylacetic acid, 5 mmol of 1H,1H,2H,2H-perfluoro-1-decylthiol and 10 mmol of acid-binding agent K2CO3 to DMF, and stir at 25°C for 1.5 h to obtain a yellow mixture; then pour the mixture into ethyl acetate, wash three times with 1 M hydrochloric acid solution, and then wash three times with pure water; collect the ethyl acetate phase, dry with anhydrous MgSO4, and remove the ethyl acetate by rotary evaporation to obtain the intermediate;

[0053] Step 2: Dissolve 1 mmol of intermediate (theoretical mass 0.628 g), 0.5 mmol of 4-dimethylaminopyridine (DMAP), and 2 mmol of 1-hexadecyl alcohol in dichloromethane (DCM), and add 2 mmol of N,N'-dicyclohexylcarbodiimide (DCC) dropwise to the DCM. After stirring at 25 °C for 18 hours, filter, remove the solvent by rotary evaporation of the solids to obtain the crude product; purify the crude product by silica gel column chromatography (PE / DCM, v / v = 100:40) to obtain the organogel factor LMOG-1.

[0054] The reaction formula is as follows:

[0055]

[0056] LMOG-1, an organic gelling factor 1 H NMR spectrum as shown Figure 2As shown, the spectral analysis results are: δ(ppm) = 7.26 (s, 4H), 4.07 (t, J = 6.7 Hz, 2H), 3.73 (s, 2H), 3.60 (s, 2H), 2.67–2.59 (m, 2H), 2.29 (tq, J = 17.8, 8.2 Hz, 2H), 1.61 (q, J = 6.9 Hz, 2H), 1.25 (s, 24H), 0.93–0.84 (m, 3H). Based on the reaction mechanism and the above spectral analysis results, the structural formula of the prepared organogel factor LMOG-1 is deduced as follows:

[0057]

[0058] 1 The analysis results of the H NMR spectrum are as follows Figure 2 As indicated by the annotations in the document.

[0059] Preparation Example 2

[0060] The rest is the same as in Preparation Example 1, except that in step (S1), 1H, 1H, 2H, 2H-perfluoro-1-heptathiols are used in equimolar substitution for 1H, 1H, 2H, 2H-perfluoro-1-decathiol, and in step (S2), 1-dodecyl alcohol is used in equimolar substitution for 1-hexadecyl alcohol, i.e., m=12, n=5, and the structural formula of the obtained organic gelling factor is:

[0061]

[0062] Preparation Example 3

[0063] The rest is the same as in Preparation Example 1, except that in step (S1), 1H, 1H, 2H, 2H-perfluoro-1-dodecathiol are used in equimolar substitution for 1H, 1H, 2H, 2H-perfluoro-1-decathiol, and in step (S2), 1-octadecyl alcohol is used in equimolar substitution for 1-hexadecyl alcohol, i.e., m=18, n=10, and the structural formula of the obtained organic gelling factor is:

[0064]

[0065] Comparative Preparation Example 1

[0066] The rest is the same as in Preparation Example 1, except that: in step (S1), 1H, 1H, 2H, 2H-perfluoro-1-tetradecylthiols are used to replace 1H, 1H, 2H, 2H-perfluoro-1-decylthiols in equal molar amounts, and in step (S2), 1-octanol is used to replace 1-hexadecylol in equal molar amounts, i.e., prepared according to the structural formula I, m=8, n=3.

[0067] Comparative Preparation Example 2

[0068] The rest is the same as in Preparation Example 1, except that in step (S1), 1H, 1H, 2H, 2H-perfluoro-1-pentanethiol are used to replace 1H, 1H, 2H, 2H-perfluoro-1-decanethiol in equal molar amounts, and in step (S2), 1-coecicosanol is used to replace 1-hexadecyl alcohol in equal molar amounts, i.e., prepared according to the structural formula I, where m=22 and n=12.

[0069] The gelling ability of the organic gelling agents prepared in the test examples and the comparative preparation examples was determined by the following method:

[0070] (S1) In a glove box filled with high-purity argon ([O2] < 0.01 ppm, [H2O] < 0.01 ppm), fluoroethylene carbonate (FEC) and methyl trifluoroethyl carbonate (FEMC) were mixed at a volume ratio of 3:7, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain the liquid electrolyte FLE.

[0071] (S2) The gelling agents prepared in the preparation example and the comparative preparation example were added to the liquid electrolyte in different proportions and heated on a heating plate at 70°C to dissolve and form a precursor solution (the concentrations of the gelling agents in the precursor solution were 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 1.0wt%, 1.5wt%, 2.0wt%, and 3.0wt% to determine the critical gel concentration). The precursor solution was cooled to room temperature and allowed to stand for 10 min. The inverted sample bottle was observed to determine whether the gel had formed. If the sample could overcome its own gravity and not fall, the gel was considered to have been successfully formed and the gel electrolyte was obtained. If the sample fell under gravity, the gel was considered not to have formed.

[0072] The gelation behavior state diagram of the organogel agent LMOG-1 prepared in Example 1 is shown in Figure 1. Figure 3 As shown. Figure 3 The results show that gelation can be achieved when the concentration of LMOG-1 is ≥0.3wt%, i.e., the critical gel concentration (CGC) is 0.3wt%. With increasing gelling factor concentration, the transparency of the gel electrolyte gradually decreases, indicating that the gel network structure becomes increasingly dense. The room temperature critical gel concentrations of the organic gelling factors prepared in each preparation example and the comparative preparation example are shown in Table 1.

[0073] Table 1 Critical gel concentration at room temperature

[0074]

[0075] As can be seen from Table 1, the organic gelling agent prepared in the preparation example can achieve gelation of liquid electrolytes within a concentration range of 0.3~3wt%.

[0076] To further analyze the gel properties of the gelling agent, a gel electrolyte (denoted as LMOG-1-FGE) prepared with LMOG-1 in the range of 0.3~2.0 wt% was tested for its storage modulus G' and loss modulus G''. The curves showing the changes in storage modulus G' and loss modulus G'' with the gelling agent content are shown in the figure below. Figure 4 As shown. Figure 4 The results show that from CGC to 1 wt%, the increases in G' and G'' of the gel electrolyte are significant, while the increases in G' and G'' are smaller when the gelling factor concentration exceeds 1 wt%. Therefore, a stable gel network can be formed when the concentration of LMOG-1 is ≥1 wt%. Under the premise of structural stability, the lower the concentration of the gelling factor and the lower the skeleton content of the gel electrolyte, the better the ionic conductivity. Therefore, to balance ionic conductivity and gel network stability, the concentration of the organic gelling factor in this invention is preferably 1.0~1.5 wt% when preparing the fluorinated gel electrolyte.

[0077] Preparation of low-skeleton-content fluorinated gel electrolytes by in-situ method

[0078] The following examples demonstrate the preparation of low-skeleton-content fluorinated gel electrolytes using a non-in-situ method to facilitate structural characterization; in-situ preparations based on the same formulation are described in the application examples below. Based on the gel performance testing and analysis of the gel factors obtained above, the content of the gel factor in the gel electrolytes in the following examples is 1 wt%. The gel factor obtained in the comparative preparation example could not produce a gel at 3.0 wt%, therefore, no further electrolyte preparation and performance testing were performed.

[0079] Example 1

[0080] (S1) In a glove box filled with high-purity argon ([O2] < 0.01 ppm, [H2O] < 0.01 ppm), fluoroethylene carbonate (FEC) and methyl trifluoroethyl carbonate (FEMC) were mixed at a volume ratio of 3:7, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain the liquid electrolyte FLE.

[0081] (S2) The organic gelling agent LMOG-1 obtained in Preparation Example 1 was added to the above liquid electrolyte (the mass ratio of LMOG-1 to liquid electrolyte was 1:99), and heated on a hot plate at 75°C until LMOG-1 dissolved to form a precursor solution (i.e., a mixture of LMOG-1, FEC, FEMC and LiTFSI, which was in liquid state at this time; calculated according to the mass fraction of 1 mol / L LiTFSI in the FEC / FEMC mixed solvent, the content of organic gelling agent was 1 wt%, the content of fluorinated lithium salt was 16.9 wt%, and the content of solvent was 82.1 wt%). The precursor solution was cooled to room temperature and allowed to stand for 30 min to fully gel, resulting in a low-skeleton fluorinated gel electrolyte (denoted as LMOG 1-FGE-1.0).

[0082] The gel-sol transition temperature T of LMOG 1-FGE-1.0 was determined by DSC. sol The temperature was 64.5℃.

[0083] Example 2-3

[0084] The rest is the same as in Example 1, except that the organogel factor LMOG-1 prepared in Example 1 is replaced with the organogel factor prepared in Example 2 and Example 3, respectively.

[0085] The resulting low-skeleton-content fluorinated gel electrolytes were designated LMOG 2-FGE-1.0 and LMOG 3-FGE-1.0, respectively. The gel-sol transition temperatures Tg of LMOG 2-FGE-1.0 and LMOG 3-FGE-1.0 were determined by DSC. sol The temperatures were 54.8℃ and 65.6℃, respectively.

[0086] In-situ preparation of low-scaffold-content fluorinated gel electrolytes and lithium batteries

[0087] To evaluate the electrochemical performance of the gel electrolyte and the lithium battery containing the gel electrolyte of the present invention, the following application examples demonstrate the in-situ preparation of a fluorinated gel electrolyte with low framework content and a lithium battery. Based on the gel performance test analysis of the organic gelling agent obtained above, the content of the organic gelling agent in the following application examples is 1 wt%.

[0088] Application Example 1

[0089] (1) Preparation of positive electrode material: Lithium iron phosphate (LFP), conductive carbon (Super P) and binder (polyvinylidene fluoride (PVDF)) were dispersed in 1-methyl-2-pyridone (NMP) at a mass ratio of 8:1:1. The mixture was then homogenized using a rotary mixer (KK-400WE, Mazerustar). The obtained slurry was transferred to a drying room and coated onto carbon-coated Al foil using a 200 μm scraper. After drying at 70 °C for 2 h, it was dried overnight in a vacuum oven at 80 °C. The dried material was cut into discs with a diameter of 10 mm to serve as positive electrode sheets (the areal loading of active material was 2.4 mg / cm²). 2 );

[0090] (2) Assembly and in-situ gelation: In a glove box, the positive electrode shell (CR2032), the above-mentioned positive electrode sheet, and the separator (Celgard 2325, 20 mm in diameter) were placed in sequence; then, a precursor solution with a gelling factor content of 1.0 wt% was prepared according to Example 1, and 150 μL of the precursor solution (i.e., a mixture of organic gelling factor LMOG-1, fluorinated solvent, and lithium salt, which is in sol state at room temperature and liquid state at 80°C) was rapidly injected on a hot stage (heated to 80°C); then, the lithium negative electrode sheet (13 mm in diameter), nickel foam (10 mm in diameter), and the negative electrode shell (CR2032) were placed in sequence, and finally, the mixture was heated to 25 Kg / cm 2 Encapsulation is performed under pressure; after encapsulation, the product is removed from the hot plate and left at room temperature for 10 h to allow the injected precursor solution to fully gel, forming a low-skeleton fluorine-containing gel electrolyte, and a lithium battery containing this gel electrolyte (denoted as Li|LMOG 1-FGE| LFP).

[0091] Application Example 2-3

[0092] The rest is the same as in Application Example 1, except that in step (2), a precursor solution with a gelling factor content of 1.0 wt% is prepared according to Examples 2-3.

[0093] For comparison, a full cell was assembled using a liquid electrolyte, denoted as Li|FLE|LFP.

[0094] It should be explained that Application Examples 1-3 correspond to the fluorinated gel electrolytes in Examples 1-3, except that the Examples use an in-situ method to prepare fluorinated gel electrolytes with low skeleton content in order to test the structure and ionic conductivity of the gel electrolyte; the Application Examples use an in-situ method to prepare lithium batteries containing fluorinated gel electrolytes with low skeleton content in order to test the electrochemical performance of the batteries.

[0095] Testing and Analysis

[0096] 1. Structural analysis of fluorinated gel electrolytes with low skeleton content

[0097] SEM image of the fluorinated gel electrolyte LMOG 1-FGE-1.0 prepared in Example 1 after dialysis and freeze-drying to remove lithium salt and solvent. Figure 5 The structure exhibits an interwoven fiber network with fiber diameters between 150 and 250 nm. This dense network structure macroscopically binds the liquid electrolyte, causing it to exhibit a gel state. Microscopically, it contains a large number of voids, allowing ions to move freely and be transported in the gel state.

[0098] The FT-IR spectra of the fluorinated gel electrolyte LMOG 1-FGE-1.0 prepared in Example 1 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are compared as follows. Figure 6 As shown. Figure 6 The results show that the characteristic peak of LMOG 1-FGE has red-shifted compared to that of lithium salt LiTFSI, indicating that the TFSI anion in lithium salt has a higher concentration. - It interacted with the gelling factor; binding Figure 5 SEM analysis confirmed that the gel network can restrict anionic TFSI. - The migration of these molecules can potentially lead to higher lithium-ion transference numbers.

[0099] 2. Testing of lithium-ion transference number and ionic conductivity

[0100] The lithium-ion transference number and ionic conductivity of the fluorinated gel electrolyte prepared in the examples were tested using a combination of chronoamperometry and electrochemical impedance spectroscopy. Specifically, a mold battery was assembled by tightly clamping a gel electrolyte disc between two stainless steel blocking electrodes. The mold battery was then connected to an electrochemical workstation. Electrochemical impedance spectroscopy was first performed before polarization, with a frequency range of 1 Hz to 1 MHz and an AC amplitude of 10 mV. Subsequently, a constant polarization voltage of 10 mV was applied to the battery, and chronoamperometry was performed, recording the current change curve over time until the current reached a steady state. Immediately after polarization, electrochemical impedance spectroscopy was performed again (under the same conditions) to characterize the interfacial stability before and after polarization.

[0101] The chronocurrent curve of the fluorinated gel electrolyte LMOG 1-FGE-1.0 prepared in Example 1 at a polarization voltage of 10 mV is shown below. Figure 7 As shown, the insets depict electrochemical impedance spectroscopy before and after polarization. Based on Figure 7Chronoamperometry curves and electrochemical impedance spectroscopy (EIS) before and after polarization were obtained. Based on the Bruce-Vincent formula, the lithium-ion transference number (L-MOG 1-FGE) was calculated to be 0.51, significantly higher than the 0.33 of the liquid electrolyte FLE. This higher L-MOG transference number indicates that lithium-ion migration dominates in this fluorinated gel electrolyte system, while TFSI... - The migration was inhibited to some extent. Combined with... Figure 6 Analysis of the FTIR spectra revealed that this was due to the interaction between the gelling factor molecules and the lithium salt anion (TFSI). - There is an interaction between the lithium ions and the anode, which restricts the migration of larger anions. This confinement effect effectively prevents anions from accumulating near the anode, thereby preventing the formation of local electric fields in the space charge region, resulting in a more uniform lithium ion flux distribution, and thus effectively preventing the growth of lithium dendrites.

[0102] Furthermore, the electronic resistance of the gel electrolyte can be calculated based on the steady-state current reached after polarization. Combined with the total resistance obtained from the impedance spectrum fitting before polarization, and after deducting the electronic conductivity, the actual ionic conductivity of the electrolyte is calculated using the formula: ionic conductivity (σ) = L / (R×S) (where L is the electrolyte thickness, S is the electrode area, and R is the bulk resistance after deducting electronic conductivity). Following the above method, the ionic conductivity of the fluorinated gel electrolytes prepared in each embodiment at room temperature was measured, and the specific results are shown in Table 2. Table 2 shows that the room temperature ionic conductivity of the low-skeleton-content fluorinated gel electrolytes prepared in this invention is all >15.0 mS / cm.

[0103] 3. Oxidation decomposition potential test

[0104] The oxidative decomposition potential of the fluorinated gel electrolyte prepared in the examples was evaluated using linear sweep voltammetry (LSV). Specifically, in an argon-filled glove box, the prepared gel electrolyte membrane was cut into 16 mm diameter discs and tightly sandwiched between a stainless steel working electrode and a lithium sheet (reference electrode) to assemble an asymmetric cell (stainless steel | gel | lithium sheet). After standing for 2 hours to allow the interface to stabilize, the cell was connected to an electrochemical workstation, and a scan rate of 0.1 mV / s was used to scan from the open-circuit potential in the forward direction to 5.5 V vs. Li. + / Li. The potential at which the current density begins to increase significantly is defined as the oxidation decomposition potential, and the specific data are summarized in Table 2. A higher oxidation decomposition potential indicates that the material has excellent high-voltage resistance and a wide electrochemical stability window.

[0105] Table 2 Ionic conductivity and oxidative decomposition potential of fluorinated gel electrolytes

[0106]

[0107] As shown in Table 2, compared with liquid electrolytes, the low-skeleton-content fluorinated gel electrolyte prepared in this invention exhibits no significant loss in ionic conductivity and oxidative decomposition potential, while simultaneously possessing both high ionic conductivity (>15.0 mS / cm) and a relatively high oxidative decomposition potential (>4.3 V vs. Li). + / Li), compatible with commercially available cathode materials (such as lithium iron phosphate (LFP) and lithium cobalt oxide (LCO).

[0108] 4. Testing the lithium dendrite suppression ability of the gel electrolyte.

[0109] To evaluate the inhibitory effect of the gel electrolyte prepared in the examples on lithium dendrite growth, a lithium-gel-electrolyte-lithium symmetric battery was used for constant current cycle life testing. Specifically, under inert gas protection, the fluorinated gel electrolyte prepared in the examples was cut into discs with a diameter of 16 mm and a thickness of 1.0 mm, sandwiched between two fresh lithium metal electrodes, and assembled into a CR2032 coin cell symmetric battery. As a comparison, a symmetric battery Li|FLE|Li containing a liquid electrolyte (FLE) was assembled using the same method. Using a battery testing system, constant current charge-discharge tests were performed on the batteries at different current densities at room temperature. High current density (2 mA / cm²) was also tested. 2 2 mAh / cm 2 The charge-discharge test at a low current density (0.2 mA / cm²) was designed to evaluate the anti-dendration capability of the gel electrolyte under high lithium-ion flux. 2 0.2 mAh / cm 2 The charge-discharge test under these conditions aims to evaluate the long-term compatibility and stability of the gel electrolyte-lithium metal interface.

[0110] The symmetric cell Li|LMOG 1-FGE|Li assembled with the fluorinated gel electrolyte in Example 1 and the symmetric cell Li|FLE|Li assembled with the liquid electrolyte (FLE) at 2 mA / cm 2 2 mAh / cm 2 The constant current cycling curve is shown in the figure. Figure 8 As shown. Figure 8In the high-current cycling curves, the symmetric battery Li|LMOG 1-FGE|Li exhibited stable cycling for 480 hours, while the symmetric batteries in the other embodiments all showed stable cycling for over 450 hours. However, the liquid symmetric battery Li|FLE|Li exhibited unstable overpotential that gradually increased, exceeding 5 V after 180 hours of cycling and triggering the safety protection setting, thus terminating the cycle. The increase in overpotential in the liquid symmetric battery can be attributed to the development of dendritic and porous lithium structures and the formation of a thicker SEI, which disrupts the integrity of the lithium electrode and increases impedance. This demonstrates that the fluorinated gel electrolyte of the present invention exhibits structural stability in high-current fast charging mode, enables rapid lithium-ion transport, and effectively suppresses lithium dendrite growth.

[0111] The symmetric cell Li|LMOG 1-FGE|Li assembled with the fluorinated gel electrolyte in Example 1 and the symmetric cell Li|FLE|Li assembled with the liquid electrolyte (FLE) at 0.2 mA / cm 2 0.2 mAh / cm 2 The constant current cycling curve is shown in the figure. Figure 9 As shown. Figure 9 The voltage curve of the symmetric cell Li|LMOG 1-FGE|Li was stable, with no significant increase in overpotential, indicating that interfacial side reactions were effectively suppressed. The symmetric cells assembled with gel electrolytes in each embodiment showed good performance at low current densities (0.2 mA / cm²). 2 0.2 mAh / cm 2 In the cyclic tests, they all showed stable cycling for more than 1200 hours.

[0112] Based on the above constant current cycling test results, it is shown that the fluorinated gel electrolyte of the present invention not only has good compatibility with lithium metal interface, but also has excellent lithium dendrite suppression ability under high current density charge and discharge conditions, demonstrating its practical potential in high energy density lithium batteries.

[0113] To verify the inhibitory effect of the gel electrolyte on lithium dendrites at the microscopic level, scanning electron microscopy was used to characterize the lithium metal surface in the symmetric cell after different number of cycles. SEM images of the lithium metal surface in the symmetric cell Li|LMOG 1-FGE|Li after 50 and 100 cycles are shown below. Figure 10 As shown, SEM images of the lithium metal surface in the symmetric battery Li|FLE|Li assembled with liquid electrolyte after 50 and 100 cycles are as follows. Figure 11 As shown. Figure 10 The results show that after 50 cycles, the lithium metal surface still maintains a relatively flat blocky accumulation structure, with no obvious dendrites or moss-like lithium. After 100 cycles, the surface remains dense and dendrite-free, and the optical photograph in the illustration shows that the lithium sheet surface still has a bright metallic luster. Figure 11The results showed that after 50 cycles, the Li anode in contact with the liquid electrolyte FLE exhibited a porous structure with a rough surface and small, loosely accumulated Li dendrites; after 100 cycles, the size of the Li dendrites on the FLE contact electrode further increased, but they were still loosely accumulated.

[0114] The above morphological characterization results and Figure 8 , Figure 9 The constant current cycling test results showed a high degree of agreement, indicating that the fluorinated gel electrolyte of the present invention has a good ability to suppress lithium dendrite growth.

[0115] 5. Lithium-ion battery cycle stability test

[0116] To further evaluate the cycle stability of the lithium battery containing the fluorinated gel electrolyte of this invention during actual use, constant current charge-discharge cycle tests were conducted on the lithium battery prepared in the application example. The cycle curves of the lithium battery Li|LMOG 1-FGE|LFP and the liquid battery Li|FLE|LFP are shown in the figure. Figure 12 As shown in the figure, the capacity of the liquid battery decays rapidly, with a capacity retention of only 55.1% after 500 cycles. In contrast, the lithium-ion battery Li|LMOG 1-FGE|LFP exhibits excellent cycle stability, retaining over 90% of its capacity after 1000 cycles. Table 3 shows the capacity retention of the lithium-ion batteries in various application examples after 1000 cycles at 1C.

[0117] Table 3 Cycle stability test of lithium batteries

[0118]

[0119] Table 3 shows that the lithium battery containing the fluorinated gel electrolyte of the present invention has excellent cycle stability, and the capacity retention rate is more than 90% after 1000 cycles.

[0120] In summary, the novel organic gelling agent of this invention can form an interaction network at low concentrations, achieving gelation of liquid electrolytes. The fluorinated gel electrolyte prepared from this organic gelling agent exhibits high ionic conductivity and an oxidation decomposition potential exceeding 4.3V, good interface compatibility with lithium metal, and excellent lithium dendrite suppression capability. Lithium batteries assembled with the fluorinated gel electrolyte of this invention demonstrate good long-cycle stability.

Claims

1. A fluorinated gel electrolyte with low skeleton content, characterized in that, It comprises an organic gelling agent, a lithium salt, and a solvent, wherein the organic gelling agent has the structure shown in Formula I; (Equation I) In Equation I, m is an integer from 12 to 18, and n is an integer from 5 to 10.

2. The low-skeleton-content fluorinated gel electrolyte according to claim 1, characterized in that, In Formula I, m is an integer from 16 to 18, and n is an integer from 8 to 10; preferably, m is 16 and n is 8.

3. The low-skeleton-content fluorinated gel electrolyte according to claim 1, characterized in that, Based on the total mass of the fluorinated gel electrolyte with low skeleton content, the content of organic gelling factor is 0.3~3.0 wt%, preferably 1.0~1.5 wt%, the content of lithium salt is 10~20 wt%, and the content of solvent is 75~88 wt%.

4. The low-skeleton-content fluorinated gel electrolyte according to claim 1, characterized in that, The organic gelling factor was prepared by the following method: 4-(2-haloethyl)phenylacetic acid, perfluoroC5-C10 alkylethyl thiol, and an acid-binding agent were dissolved in a first solvent and stirred to react. The crude product was washed, dried, and rotary evaporated to obtain an intermediate. The intermediate, C12-C18 alkyl alcohol, catalyst, and dehydrating agent were dissolved in a second solvent and reacted. The mixture was then filtered, and the solids were rotary evaporated to obtain a crude product. The crude product was purified to obtain the organic gelling factor shown in Formula I.

5. The low-skeleton-content fluorinated gel electrolyte according to claim 4, characterized in that, The molar ratio of 4-(2-haloethyl)phenylacetic acid, perfluoroC5-C10 alkylethyl thiol, and the acid-binding agent is 1:(1~1.2):(1.8~2.5); preferably, the 4-(2-haloethyl)phenylacetic acid is selected from at least one of 4-(bromoethyl)phenylacetic acid and 4-(chloroethyl)phenylacetic acid; the perfluoroC5-C10 alkylethyl thiol is selected from 1H, 1H, 2H, 2H-perfluoro-1-heptyl thiol, 1H, 1H, 2H, 2H-perfluoro-1-octyl thiol, 1H, 1H, 2H, 2H-perfluoro-1-nonyl thiol, 1H, 1H, 2H, 2H-perfluoro-1-decyl thiol, 1H, 1H, 2H, 2H-perfluoro-1 -At least one of undecylthiol, 1H, 1H, 2H, 2H-perfluoro-1-dodecylthiol; the acid-binding agent is selected from at least one of sodium carbonate (Na2CO3) and potassium carbonate (K2CO3); the first solvent is an aprotic polar solvent selected from at least one of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC); the stirring reaction conditions are: reaction at 20~40℃ for 1~2 h; the washing method is: dissolving the intermediate crude product in ethyl acetate, washing with dilute hydrochloric acid, then washing with pure water, and collecting the ethyl acetate phase; the drying is: drying the ethyl acetate phase with MgSO4 (to remove water); and / or, The molar ratio of the intermediate, C12-C18 alkyl alcohol, catalyst, and dehydrating agent is 1:(1.5~2.0):(0.3~0.5):(1.5~2.5); the catalyst is selected from at least one of 4-dimethylaminopyridine (DMAP) and 4-pyrrolidinylpyridine (PPY); the dehydrating agent is selected from at least one of N,N'-dicyclohexylcarbodiimide (DCC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), and N,N'-diisopropylcarbodiimide (DIC); the second solvent is dichloromethane; the reaction conditions are: reaction at 20~40℃ for 15~24h; the purification treatment is: the crude product is subjected to silica gel column chromatography.

6. The low-skeleton-content fluorinated gel electrolyte according to claim 1, characterized in that, The lithium salt is a fluorinated lithium salt, specifically selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium nitrate, and lithium perchlorate; the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, fluoroethylene carbonate, dimethyl fluorocarbonate, methyl trifluoroethyl carbonate, fluoropropylene carbonate, diethyl fluorocarbonate, dimethyl difluorocarbonate, dimethyl difluorocarbonate, diethylene difluorocarbonate, and trifluoroethylene carbonate, preferably at least one of fluoroethylene carbonate, dimethyl fluorocarbonate, methyl trifluoroethyl carbonate, fluoropropylene carbonate, diethyl fluorocarbonate, dimethyl difluorocarbonate, diethylene difluorocarbonate, and trifluoroethylene carbonate (TFEC).

7. The low-skeleton-content fluorinated gel electrolyte according to claim 1, characterized in that, The gel-sol transition temperature of the low-skeleton-content fluorinated gel electrolyte is 50~70℃.

8. The method for preparing the low-skeleton content fluorinated gel electrolyte according to any one of claims 1-7, characterized in that, Includes the following steps: (S1) Mix the solvent and lithium salt according to the specified ratio to obtain a liquid electrolyte; (S2) Add the organic gelling factor to the liquid electrolyte, heat to dissolve, and then cool to room temperature and let stand to obtain a fluorine-containing gel electrolyte with low skeleton content. Further, in step (S2), the heating is performed at 70~90℃; the settling time is 10~30min.

9. A lithium battery, characterized in that, The lithium battery includes a positive electrode, a separator, a negative electrode, and a low-scaffold-content fluorinated gel electrolyte as described in any one of claims 1-7.

10. An organic gelling agent for use in gel electrolytes, having the following structural formula I: (Equation I) In Equation I, m is an integer from 12 to 18, and n is an integer from 5 to 10.

Images