a kind of sp 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li, its preparation method and application

Abstract

This invention discloses a sp 3 This invention relates to hybrid boron-based single-ion polymer lithium salt DDBSB-Li, its preparation method, and its applications, belonging to the field of lithium metal battery technology. The invention utilizes calcium 2,5-dihydroxybenzenesulfonate, lithium carbonate, and lithium borohydride (Li₂O₃). + BH4 ‑ Using tetrahydrofuran solution as a raw material, a sp... was prepared by cross-linking reaction. 3 A high-conductivity single-ion polymer nanofiber electrolyte was prepared by electrospinning a hybrid boron-based single-ion polymer lithium salt (DDBSB-Li) blended with PVDF-HFP. The es-DDBSB-Li / 1M LiPF6in EC / DMC electrolyte of this invention exhibited the best rate performance (discharge specific capacities of the three electrolytes at 3C were 135.3 mAh / g, 91.3 mAh / g, and 95.6 mAh / g, respectively). After rate testing, the cycle performance of the corresponding batteries at 1C was further tested. The first-cycle discharge specific capacities at 1C were 156.1 mAh / g, 108.9 mAh / g, and 110.0 mAh / g, respectively. The es-DDBSB-Li / 1M LiPF6in EC / DMC electrolyte showed the best discharge capability.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a sp 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li, its preparation methods and applications, particularly in the preparation of high-conductivity lithium sulfonate / sp 3 Application of boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li. Background Technology

[0002] The conductivity mechanism of polymer electrolytes is highly dependent on the structure and chemical properties of the host polymer, which has been extensively explored in previous research. A simple method to improve ionic conductivity is to introduce more salt to increase the lithium salt concentration, thereby increasing the number of mobile ions. Furthermore, to accelerate lithium-ion transport, the ion association between anions and lithium ions should be reduced by expanding the charge distribution of the anionic moiety. 3 Hybrid boron is a lithium salt with strong charge delocalization. Its tetrahedral structure disperses the electronegativity on the surface of boron atoms, facilitating the dissociation of lithium ions after interaction with the polymer chain. Therefore, it is widely used in high-performance single-ion polymer electrolytes. The introduction of aromatic conjugated groups leads to the delocalization of the partially negative charge of the anion, increasing ionic conductivity. Polymer networks with three-dimensional cross-linked structures of borate anions are a preferred choice for artificial protective layers because the three-dimensional cross-linked structure possesses excellent mechanical strength and dimensional stability.

[0003] Based on the above reasons, this application is made in order to improve the low conductivity of lithium sulfonate type single-ion polymer electrolytes in the prior art. Summary of the Invention

[0004] Based on the above reasons, and in view of the problems or defects existing in the prior art, the purpose of this invention is to provide a sp 3 The hybrid boron-based single-ion polymer lithium salt DDBSB-Li, its preparation method, and its application solve or at least partially solve the aforementioned technical defects in the prior art.

[0005] To achieve one of the above-mentioned objectives of the present invention, the technical solution adopted by the present invention is as follows:

[0006] a kind of sp 3 A method for preparing hybrid boron-based single-ion polymer lithium salt DDBSB-Li, the method specifically including the following steps:

[0007] (1) Calcium 2,5-dihydroxybenzenesulfonate and lithium carbonate were added to deionized water in sequence according to the ratio and stirred for 10-14 h. After the reaction was completed, the product was filtered to remove the solvent in the filtrate and dried to obtain lithium dihydroxybenzenesulfonate (DDBS-Li).

[0008] (2) Dissolve the DDBS-Li obtained in step (1) in anhydrous tetrahydrofuran (THF) to obtain a DDBS-Li solution; dilute the lithium borohydride tetrahydrofuran (LiBH4 / THF) solution to obtain a diluted LiBH4 / THF solution; slowly add the diluted LiBH4 / THF solution dropwise to the DDBS-Li solution according to the ratio, and heat the resulting mixture to 40-50℃ under an inert atmosphere for 5-7 hours; after the reaction is completed, filter, wash, and dry the obtained product to obtain the sp 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li.

[0009] Furthermore, in the above technical solution, the molar ratio of calcium 2,5-dihydroxybenzenesulfonate to lithium carbonate in step (1) is 1:1.

[0010] Furthermore, in the above technical solution, the amount of deionized water used in step (1) is not specifically limited, as long as it can achieve uniform dissolution of calcium 2,5-dihydroxybenzenesulfonate and lithium carbonate. In a preferred embodiment of the present invention, the ratio of calcium 2,5-dihydroxybenzenesulfonate to deionized water is 0.01 mol: 80 mL.

[0011] Furthermore, in the above technical solution, the stirring reaction time in step (1) is preferably 12 hours.

[0012] Furthermore, in the above technical solution, the concentration of the DDBS-Li solution in step (2) is 0.1-0.5 mol / L. In a preferred embodiment of the present invention, the concentration of the DDBS-Li solution is 0.2 mol / L.

[0013] Further, in the above technical solution, the ratio of DDBS-Li to lithium borohydride tetrahydrofuran solution in step (2) is (1-5) mmol:(1-3) mL. In a preferred embodiment of the present invention, the ratio of DDBS-Li to lithium borohydride tetrahydrofuran is 4 mmol:1 mL.

[0014] Furthermore, in the above technical solution, the dripping time of the LiBH4 / THF solution in step (2) is 30-60 min. In a preferred embodiment of the present invention, the dripping time is 40 min.

[0015] Furthermore, in step (2) of the above technical solution, the inert gas is preferably argon.

[0016] Furthermore, in a preferred embodiment of the present invention, step (2) of the above technical solution involves a reaction temperature of 45°C and a reaction time of 6 hours.

[0017] A second objective of this invention is to provide sp prepared using the method described above. 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li.

[0018] A third object of the present invention is to provide sp prepared by the method described above. 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li in the preparation of high-conductivity lithium sulfonate / sp 3 Application of boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li.

[0019] A high conductivity lithium sulfonate / sp 3 The preparation method of boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li is as follows:

[0020] According to the ratio, sp... 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) were dissolved in N,N-dimethylformamide (DMF) to form a homogeneous solution; the resulting solution was then spun into a film and dried to obtain the high-conductivity lithium sulfonate / sp. 3 Boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li.

[0021] Furthermore, in the above technical solution, the sp 3 The mass ratio of hybrid boron-based single-ion polymer lithium salt DDBSB-Li to PVDF-HFP is 1:2.

[0022] Furthermore, in the above technical solution, the mass fraction of the homogenized solution is 15-20%.

[0023] A fourth objective of this invention is to provide a high-conductivity lithium sulfonate / sp prepared by the method described above. 3 Boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li.

[0024] The fifth object of the present invention is to provide a high-conductivity lithium sulfonate / sp prepared by the method described above. 3 Application of boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li in lithium metal batteries.

[0025] A lithium metal battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is the high-conductivity lithium sulfonate / sp described above in this invention. 3 Boron-lithium dual-ion nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li.

[0026] Furthermore, in the above technical solution, the positive electrode sheet includes a positive electrode active material, a conductive material, and a binder. The positive electrode active material is lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), or lithium nickel cobalt manganese oxide (LiNi). x Co y Mn z Any one of O2 and lithium manganese oxide (LiMn2O4).

[0027] Preferably, in the above technical solution, the preparation method of the positive electrode sheet includes the following steps: mixing the positive electrode active material, conductive material, and binder at a mass ratio of 8:1:1, using N,N-dimethylpyrrolidone as a solvent, thoroughly grinding to form a slurry, then coating it onto aluminum foil using a wet film preparation device, and vacuum drying at 80°C for 12 hours. After drying, using a cutting tool, cutting the aluminum foil coated with the sample into ready-made electrode sheets.

[0028] Furthermore, in the above technical solution, the negative electrode is a lithium metal disc.

[0029] Furthermore, in the above technical solution, the electrolyte is a LiPF6-EC / DMC electrolyte system or an EC / DMC electrolyte system.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) This invention uses calcium 2,5-dihydroxybenzenesulfonate, lithium carbonate, and lithium borohydride (Li + BH4 - Using tetrahydrofuran solution as a raw material, a sp... was prepared by cross-linking reaction. 3 A hybrid boron-based single-ion polymer lithium salt (DDBSB-Li) was blended with PVDF-HFP and then electrospinned to prepare a high-conductivity single-ion polymer nanofiber electrolyte.

[0032] (2) The es-DDBSB-Li / 1M LiPF6 in EC / DMC electrolyte of this invention exhibited the best rate performance (the discharge specific capacities of the three electrolytes at 3C rate were 135.3 mAh / g, 91.3 mAh / g, and 95.6 mAh / g, respectively). After the rate test, the cycle performance of the batteries corresponding to the three electrolytes at 1C rate was further tested. The discharge specific capacities in the first week at 1C were 156.1 mAh / g, 108.9 mAh / g, and 110.0 mAh / g, respectively. The es-DDBSB-Li / 1M LiPF6 in EC / DMC electrolyte showed the best discharge capability. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The reaction equation for the preparation of lithium dihydroxybenzenesulfonate (DDBS-Li) in Example 1 is as follows:

[0035] Figure 2 sp in Example 1 3 The reaction equation for the preparation of the hybrid boron-based single-ion polymer DDBSB-Li;

[0036] Figure 3 This is a schematic diagram showing the preparation process and structure of the single-ion polymer nanofiber es-DDBSB-Li in Example 2;

[0037] Figure 4 NMR spectra of DDBSB-Li prepared in Example 1. (a) Proton NMR spectrum; (b) Boron NMR spectrum;

[0038] Figure 5 The infrared spectrum of DDBSB-Li prepared in Example 1;

[0039] Figure 6 SEM images of the es-DDBSB-Li films prepared in Example 2 at different magnifications: (a) 10000, (b) 30000, (c) 50000; (de) SEM image of es-DDBSB-Li nanofibers and corresponding EDX elemental mapping images; (f) B element, (g) C element, (h) O element, (i) S element;

[0040] Figure 7High flexibility of es-DDBSB-Li membrane under different bending conditions: (a) optical photographs, (b) winding, (c) folding, (d) twisting; (ef) flame retardant effect of PP membrane and es-DDBSB-Li membrane; (gh) contact angle between the membrane and commercial electrolyte: (g) PP membrane after 15s, after 30s, (h) es-DDBSB-Li membrane after 15s, after 30s;

[0041] Figure 8 (a) Tensile curve of es-DDBSB-Li film; (b) TG curve; (c) DSC curve; (d) Thermal shrinkage images of PP film and es-DDBSB-Li film;

[0042] Figure 9 Time-current curves of the insertion impedance plot: (a) PP / 1M LiPF6 in EC / DMC electrolyte, (b) es-DDBSB-Li-s electrolyte, (c) es-DDBSB-Li-1M LiPF6 in EC / DMC electrolyte; (d) Long-term constant current cycling test of lithium symmetric batteries with three electrolytes.

[0043] Figure 10 The morphology of the lithium sheet after long-term constant current testing of the original lithium sheet, PP / 1M LiPF6 in EC / DMC, es-DDBSB-Li-s, and es-DDBSB-Li / 1MLiPF6 in EC / DMC electrolytes: (ad) optical photograph, (eh) planar image, (il) cross-section.

[0044] Figure 11 Comparison of electrochemical performance of batteries assembled in commercial electrolyte systems using es-DDBSB-Li electrolyte and PP membrane: (a) linear sweep voltammetry curves; (b) ionic conductivity; (c) impedance diagrams at room temperature; (d) rate performance of Li / LiFePO4 batteries at room temperature; (e) 1C cycle performance at room temperature. Detailed Implementation

[0045] To address the low conductivity issue of lithium sulfonate-type single-ion polymer electrolytes, this invention introduces sp... 3 Hybrid boron-based single ions are proposed to improve ionic conductivity and suppress lithium dendrites by achieving high lithium ion concentration through a double lithium salt structure, thereby improving the application of single-ion polymer electrolytes in lithium metal batteries.

[0046] This invention uses calcium dihydroxybenzenesulfonate, lithium carbonate, and lithium borohydride (Li + BH4 - Using tetrahydrofuran solution as a raw material, a sp... was prepared by cross-linking reaction. 3A high-conductivity single-ion polymer nanofiber electrolyte was prepared by electrospinning of hybrid boron-based single-ion polymer lithium salt (DDBSB-Li) blended with PVDF-HFP. The physicochemical properties of the electrolyte and its electrochemical performance in lithium metal batteries were investigated.

[0047] The present invention will be further described in detail below through implementation examples. These implementation examples are carried out based on the technology of the present invention. Detailed implementation methods and specific operating procedures are provided to illustrate the inventiveness of the present invention, but the scope of protection of the present invention is not limited to the following implementation examples.

[0048] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless otherwise stated, the numerical parameters listed in the specification are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0049] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0050] Example 1

[0051] One sp in this embodiment 3 The preparation method of hybrid boron-based single-ion polymer lithium salt DDBSB-Li consists of two steps, as follows: Figure 1 and Figure 2 As shown, the method specifically includes the following steps:

[0052] (1) Add 4.22g (0.01mol) calcium 2,5-dihydroxybenzenesulfonate and 0.754g (0.01mol) lithium carbonate to 80mL of water, mix and stir for 12h, filter out the generated CaCO3 precipitate, remove the solvent from the filtrate, and dry to obtain lithium 2,5-dihydroxybenzenesulfonate (DDBS-Li).

[0053] (2) First, 3.92 g (20 mmol) of lithium dihydroxybenzenesulfonate (DDBS-Li) was dissolved in 100 mL of anhydrous tetrahydrofuran (THF). Then, 5 mL of a 2 M LiBH4 / THF solution was diluted with 40 mL of anhydrous THF in a constant pressure funnel, and then added dropwise to the above solution over 40 min. The reaction was maintained at 45 °C for 6 h under an argon atmosphere. After filtration, the reaction solution was washed continuously overnight with anhydrous acetonitrile to obtain the product. The prepared product was finally dried under vacuum at 80 °C and named DDBSB-Li.

[0054] Example 2

[0055] The es-DDBSB-Li nanofiber membrane of this embodiment is prepared by electrospinning, and the electrospinning process is as follows: Figure 3 As shown, it is prepared using the following method, with the steps as follows:

[0056] Nanofiber electrolyte membranes were prepared using an electrospinning process. The polymer lithium salt product DDBSB-Li prepared in Example 1 was dissolved in a certain amount of N,N-dimethylformamide (DMF) at a mass ratio of 1:2 to prepare a homogeneous solution with a mass fraction of 18%. This solution was then spun into a membrane at a receiving distance of 15 cm, a voltage of 29 kV, and a spray rate of 2 μL / min. After drying at 60 °C for 12 h, the membrane was cut into 19 mm diameter diaphragms and then dried in a vacuum oven at 80 °C for 24 h. Finally, the resulting electrolyte membrane (denoted as es-DDBSB-Li) was placed in an argon-filled glove box for later use.

[0057] Structural characterization

[0058] Nuclear magnetic resonance analysis was performed on the product DDBSB-Li synthesized in Example 1, as follows: Figure 4 As shown. Figure 4 a and 4b represent the 1H NMR and boron NMR analyses of the product, respectively. Specifically, 1 Integral area in HNMR: H a (6.53ppm):H b (6.57ppm):H c (6.86ppm) = 0.96:1.01:1.00. 11 The boron NMR analysis used boron trifluoride diethyl ether solution (BF3·Et2O) as an internal standard. Peaks corresponding to different chemical shifts in the boron spectrum indicated the presence of boron atoms in different chemical environments. Apart from the internal standard, there was only one peak at 8.7 ppm (less than 10), indicating that the boron atoms in the polymer are sp2 hybridized. 3 Hybrid, and has only one structure.

[0059] Further investigation was conducted into the structure of the product DDBSB-Li synthesized in Example 1, such as... Figure 5 The infrared spectrum shows that the polymerized material is at 3400 cm⁻¹. -1 The disappearance of the nearby phenolic hydroxyl peak, with a wavenumber of 1489 cm⁻¹ in DDBSB-Li. -1 and 1448cm -1 The infrared absorption peak at this point belongs to the stretching vibration peak of CH on the benzene ring; the wavenumber is 1080 cm⁻¹. -1 and 1026cm -1The peaks at these locations belong to the symmetric stretching vibration peaks of -SO2-. The characteristic absorption at 1200 cm⁻¹... -1 Up to 1400cm -1 The formation of the new peak confirms the formation of the BO bond.

[0060] The molecular weight of DDBSB-Li was analyzed by gel permeation chromatography (GPC), as shown in Table 1 below. For DDBSB-Li, the number-average molecular weight was 91,927, the weight-average molecular weight was 111,990, and the polydispersity index (M) was measured. w / M n The value was 1.23. A stable framework provides good support and abundant binding sites for anion anchoring. Based on these characterization results, the synthesized product is the target product.

[0061] Table 1 Gel permeation chromatography

[0062]

[0063] This invention uses field emission scanning electron microscopy to characterize the microstructure of the diaphragm. The gold sputtering time is 60 s. Before testing, the diaphragm is vacuum dried at 80°C for 24 h. The membrane flexibility properties are recorded using a camera. The wetting angle is measured using a wetting angle meter, and the wetting angle is read directly from the instrument.

[0064] Nanofiber membrane morphology

[0065] Figure 6 The images show SEM images and corresponding EDX images of the es-DDBSB-Li membrane. The average diameter of its nanofibers is approximately 100 nm. The SEM images reveal a highly open, interlocking, high-porosity network structure. Due to the unique cross-linked network, the space between the polymer chains induces high solvent absorption, which is beneficial for achieving high ionic conductivity. Figure 6 ei is corresponding to Figure 6 EDX elemental mapping analysis of the d-film showed that boron was derived from DDBSB-Li and sulfur from sulfonic acid groups. The uniform distribution of these elements indicates thorough mixing between DDBSB-Li and PVDF-HFP.

[0066] Diaphragm physical property characterization

[0067] pass Figure 7 It can intuitively demonstrate the physical properties of the es-DDBSB-Li membrane. The flexibility of the polymer electrolyte is very important for the cycle life and other performance of the battery. Due to the long-term effects of environmental factors such as light and heat, as well as external forces such as stretching, twisting, cutting, and extrusion, the membrane material will inevitably be damaged in practical applications, affecting the battery's output capacity and service life, and seriously reducing the battery's reliability and durability. Figure 7 ad represents the performance of the es-DDBSB-Li membrane under different bending conditions in its dry state. Comparing the flame retardant properties of commercial PP membranes and es-DDBSB-Li membranes, it is evident that the latter exhibits self-extinguishing behavior after ignition and does not shrink as rapidly as the PP membrane. Figure 7 (e,f) The excellent flame-retardant properties originate from the boron element in the separator. This is beneficial for solving the safety issues of lithium metal batteries. Good wettability facilitates the affinity between the separator and the electrolyte, thereby increasing interfacial compatibility. The wettability of the separator to commercial electrolytes is characterized by dynamic contact angle testing. The adsorption of electrolytes by the es-DDBSB-Li membrane and commercial PP membrane can be compared from... Figure 7 The results show that the PP membrane wets very slowly with the electrolyte, with a contact angle of 68.0° at 15s and 67.7° at 30s. In contrast, the es-DDBSB-Li membrane exhibits excellent wettability with the electrolyte, with a contact angle as low as 7.0° after 30s of wetting.

[0068] The thermal stability of the material was analyzed using a thermogravimetric analyzer under a nitrogen atmosphere and a heating rate of 10℃ / min. -1 The test temperature range is 30 to 800℃. Differential scanning calorimetry was used under a nitrogen flow, with heating and cooling rates of 10℃ / min. -1 When the temperature changes from 30-300℃ or -80-100℃, the heat absorption and release behavior of the material is tested.

[0069] Figure 8 Figure a shows the tensile curves of the dry and wet films (after immersion in electrolyte for 20 hours) of the es-DDBSB-Li mixture. The tensile strengths of the dry and wet films are 4.02 MPa and 2.48 MPa, respectively; this is because the cross-linked network of the polymer electrolyte can improve the poor mechanical properties of the spun film to some extent. Furthermore, the spun film exhibits good ductility, with elongations of 24.4% and 48.8% in the dry and wet films, respectively, which can accommodate the volume changes of the lithium anode during cycling. The excellent flame-retardant properties and thermal stability of the separator improve the safety of battery use. Figure 8 From the DSC curves, it can be observed that the PVDF-HFP spun membrane and PP membrane have obvious endothermic peaks at 154.2℃ and 161.7℃, respectively. However, no endothermic peak was observed in DDBSB-Li within this test temperature range, indicating that the material has not yet melted below 250℃, and its higher melting point ensures the integrity of the electrolyte membrane. The membrane was placed on heating plates at different temperatures (25℃ to 180℃) for 20 minutes to investigate its thermal shrinkage stability. Figure 8 Image d shows the heat shrinkage of the two types of membranes. At temperatures above 100°C, the commercial PP membrane exhibits severe shrinkage and deformation, while the es-DDBSB-Li membrane demonstrates better thermal stability.

[0070] Lithium-ion transference number, lithium stripping / electroplating performance, and lithium metal anode morphology

[0071] The EIS test of this invention was performed on a Li / LFP battery using a VMP3 electrochemical workstation, with a scan range of 100 kHz to 10 mHz. LSV testing was also performed on the VMP3 electrochemical workstation using an assembled Li / SS (stainless steel pad) battery. The LSV test conditions were: scan rate of 5 mV / s, onset potential of 2 V, termination potential of 6 V, and data recording interval of 0.0002 s.

[0072] The lithium-ion transport number (t) of several electrolytes was measured using the steady-state current method at room temperature after assembling a lithium symmetric cell. Li + The preparation process of the LiFePO4 positive electrode is as follows: A certain amount of active material (LiFePO4) in a mass ratio of 7:2:1, acetylene black (AB) conductive additive, and PVDF binder are weighed and dissolved in a calculated amount of N-methylpyrrolidone (NMP) to form a slurry. This slurry is then cast onto aluminum foil using a coating machine. Subsequently, the coated aluminum foil is dried in a forced-air oven at 60°C for 12 hours, then cut into 15nm discs for use as the positive electrode of the button cell, and transferred to a vacuum oven at 80°C for overnight drying. The electrolyte is a 1M LiPF6 EC / DMC (1:1, v / v) solution or a pure EC / DMC (1:1, v / v) solution.

[0073] like Figure 9 As shown in the diagram, detailed test results are summarized in Table 2. The t-values ​​of the es-DDBSB-Li-s (es-DDBSB-Li︱EC / DMC single-ion system) electrolyte are... Li + The value is 0.71, indicating its single-ion conduction behavior. Figure 9 b). Conversely, the t of PP / 1M LiPF6 inEC / DMC electrolyte Li + The value is relatively low, at 0.38. Figure 9 a). It is worth noting that the t of es-DDBSB-Li-1M LiPF6 in EC / DMC electrolyte Li + It is 0.61 ( Figure 9 c) Increasing the lithium-ion transference number of the electrolyte through single-ion conduction is an effective method.

[0074] Table 2. Measured values ​​of the corresponding lithium-ion transference numbers.

[0075]

[0076]

[0077] The effects of lithium-ion transference number on stripping / electroplating performance and lithium dendrite growth on the lithium metal anode were investigated using constant current testing with a lithium symmetric cell. Figure 9 As shown in d, when the current density is 2.5 mA / cm² 2 At that time, the polarization voltage of PP / 1MLiPF6 in EC / DMC electrolyte was the largest and unstable; after cycling, pure metallic lithium will have a large number of lithium dendrites growing and dead lithium accumulating on the surface, resulting in increased polarization and poor long-term cycling performance; es-DDBSB-Li-s electrolyte is good at suppressing concentration polarization, exhibiting the smallest polarization voltage, and can still maintain a fairly stable voltage after cycling for up to 2000h, effectively suppressing the growth of lithium dendrites.

[0078] A lithium-ion symmetric battery that had undergone long-term constant current cycling was disassembled, and the dendrite growth on its lithium metal surface was studied. The results are as follows: Figure 10 As shown, comparative analyses were performed using optical photographs, SEM surface images, and cross-sectional images. The microstructure of the separator was characterized using field emission scanning electron microscopy (FESEM) with a gold sputtering time of 60 s. Prior to testing, the separator was vacuum-dried at 80°C for 24 h. The original lithium sheet surface was smooth and flat, while severe dendrite growth was observed in the PP / 1M LiPF6 in EC / DMC electrolyte after short-term constant current cycling, exhibiting an uneven, grooved appearance. Volume expansion was also observed in the cross-section. This lithium dendrite growth can penetrate the separator or alter the volume of the negative electrode material, causing significant strain and potentially leading to battery safety issues. In contrast, the es-DDBSB-Li-s electrolyte maintained a certain degree of flatness and volume stability on the lithium metal surface even after long-term constant current cycling. SEM images showed some localized areas of the lithium surface covered with a thin layer of spun nanofibers, which may have inhibited lithium dendrite growth. Thanks to the Lewis acid-base interaction between boron atoms and anions in lithium salt, lithium ions are uniformly distributed on lithium metal, thereby improving the interfacial stability between es-DDBSB-Li and lithium metal.

[0079] Electrochemical performance

[0080] The ionic conductivity of this invention can be used to test the ease of charge flow in a battery, and it often changes with temperature. The ionic conductivity of the membrane can be determined using EIS in a VMP3 electrochemical workstation, assembling a SS|membrane|SS battery, setting the frequency to 1MHz~1Hz and the voltage to 5mV. The ionic conductivity is calculated using the following formula:

[0081]

[0082] Where l is the diaphragm thickness (cm), R is the measured impedance (Ω), and A is the effective contact area (cm²). 2LSV was performed on a VMP3 electrochemical workstation. Li / SS (stainless steel gasket) batteries were assembled. The LSV test conditions were: scan rate of 5 mV / s, onset potential of 2 V, termination potential of 6 V, and data recording interval of 0.0002 s. This experiment was conducted on a LAND testing system to evaluate the practical application of the separator as a high-performance lithium metal battery separator by constructing a LiFePO4|Li coin cell (model 2025). Charge-discharge tests were first performed at different rates, with 6 cycles at each rate. Then, a suitable rate was selected for long-term cycle performance testing.

[0083] The electrochemical stability window (ESW) can intuitively measure the electrochemical stability of an electrolyte. From the linear sweep voltammetry (LSV) curve, it can be seen that the oxidation peak of the es-DDBSB-Li-s (es-DDBSB-Li︱EC / DMC single-ion system) electrolyte occurs at a voltage around 4.48 V, and no oxidation peak appears between 2.5 V and 4.2 V. This indicates that the electrolyte is electrochemically inert within this operating voltage range and no electrochemical reactions occur. The ionic conductivity of three electrolytes was tested at temperatures ranging from 25℃ to 80℃. Figure 11 b. While the es-DDBSB-Li-s electrolyte exhibits the lowest ionic conductivity among the three, it should be noted that its conductivity at room temperature is quite close to that of the commercially available PP-1M LiPF6 in EC-DMC electrolyte; when a commercial electrolyte is added, from Figure 11 As can be seen intuitively, the interfacial resistance of the es-DDBSB-Li electrolyte is significantly reduced, which is related to... Figure 11 The significantly improved ionic conductivity of DDBSB is consistent with that of commercial PP systems; this is due to the fact that DDBSB... - Boron atoms undergo charge delocalization through covalent bonding with electron-withdrawing groups, thereby weakening the electrostatic interaction between lithium ions and anions. Simultaneously, the ionic conductivity of es-DDBSB-Li / 1M LiPF6in EC / DMC decreases from 2.22 × 10⁻⁶. - 3 S / cm (25℃) increased to 4.86×10 -3 S / cm (80℃). In addition, the activation energy (E) a Li used for evaluating electrolytes + Transfer capability, involving Li + Dissociation and migration. Smaller E a The value indicates the transfer of Li through the electrolyte. + The required energy is relatively low. The linear relationship between the logarithm of ionic conductivity and the reciprocal of temperature roughly conforms to the Arrhenius equation, and E can be calculated through fitting. aValue. E values ​​of PP system and es-DDBSB-Li-s electrolyte. a The values ​​were 14.286 kJ / mol and 8.08 kJ / mol, respectively. A low activation energy can increase the mobility of polymer segments, thereby increasing ionic conductivity. The rate capability and cycle performance of the assembled Li / LiFePO4 battery were investigated. Figure 11 d、 Figure 11 As shown in Figure e, the discharge specific capacities of the es-DDBSB-Li / 1M LiPF6 in EC / DMC electrolyte, PP / 1M LiPF6 in EC / DMC electrolyte, and es-DDBSB-Li-s electrolyte at 0.1C rate are 166.4 mAh / g, 159.6 mAh / g, and 158.2 mAh / g, respectively. The rate performance of the es-DDBSB-Li-s electrolyte is slightly better than that of the PP / 1M LiPF6 in EC / DMC electrolyte in subsequent high-rate tests. The es-DDBSB-Li / 1M LiPF6 in EC / DMC electrolyte exhibits the best rate performance (discharge specific capacities of the three electrolytes at 3C rate are 135.3 mAh / g, 91.3 mAh / g, and 95.6 mAh / g, respectively). After the rate tests, the cycle performance of the batteries corresponding to the three electrolytes at 1C rate was further tested. The first-cycle discharge specific capacities at 1C rate are 156.1 mAh / g, 108.9 mAh / g, and 110.0 mAh / g, respectively. The es-DDBSB-Li / 1M LiPF6 in EC / DMC electrolyte exhibited the best discharge capacity, while the PP system showed the worst cycle performance and the lowest coulombic efficiency among the three. After 300 cycles, the PP system showed significant capacity decay, while the Li / LiFePO4 battery corresponding to the es-DDBSB-Li-s electrolyte demonstrated excellent cycle stability. The short cycle life may be related to the high polarization voltage of the battery corresponding to the electrolyte. Figure 9 d) There is a certain relationship.

Claims

1. A kind of sp 3 A method for preparing hybrid boron-based single-ion polymer lithium salt DDBSB-Li, characterized in that: The method specifically includes the following steps: (1) Calcium 2,5-dihydroxybenzenesulfonate and lithium carbonate were added to deionized water in sequence according to the ratio, and the mixture was stirred and reacted for 10-14 h. After the reaction was completed, the product was filtered to remove the solvent in the filtrate and dried to obtain lithium dihydroxybenzenesulfonate DDBS-Li. (2) Dissolve the lithium dihydroxybenzenesulfonate (DDBS-Li) obtained in step (1) in anhydrous tetrahydrofuran (THF) to obtain a DDBS-Li solution; dilute the lithium borohydride tetrahydrofuran (LiBH4 / THF) solution to obtain a diluted LiBH4 / THF solution; slowly add the diluted LiBH4 / THF solution dropwise to the DDBS-Li solution according to the specified ratio, and heat the resulting mixture to 40-50°C under an inert atmosphere. o The reaction was carried out at a constant temperature for 5-7 hours. After the reaction was completed, the product was filtered, washed, and dried to obtain the sp. 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li.

2. The method according to claim 1, characterized in that: The molar ratio of calcium 2,5-dihydroxybenzenesulfonate to lithium carbonate in step (1) is 1:

1.

3. The method according to claim 1, characterized in that: The volume ratio of DDBS-Li to lithium borohydride tetrahydrofuran solution in step (2) is (1-5) mmol: (1-3) mL; The concentration of the lithium borohydride tetrahydrofuran solution is 2M.

4. The sp prepared by the method according to any one of claims 1-3 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li.

5. The sp prepared by the method according to any one of claims 1-3 3 Application of hybrid boron-based single-ion polymer lithium salt DDBSB-Li in the preparation of nanofiber single-ion polymer electrolyte membranes es-DDBSB-Li.

6. A method for preparing a nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li, characterized in that: The steps are as follows: The sp prepared by the method according to any one of claims 1-3 is sequentially mixed according to the specified proportions. 3 Hybrid boron-based single-ion polymer lithium salt DDBSB-Li and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) are dissolved in N,N-dimethylformamide (DMF) to form a homogeneous solution; then the resulting solution is spun into a film and dried to obtain the nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li.

7. The method according to claim 6, characterized in that: The sp 3 The mass ratio of hybrid boron-based single-ion polymer lithium salt DDBSB-Li to PVDF-HFP is 1:

2.

8. The nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li prepared by the method of claim 6 or 7.

9. The application of the nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li prepared by the method of claim 6 or 7 in lithium metal batteries.

10. A lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is a nanofiber single-ion polymer electrolyte membrane es-DDBSB-Li prepared by the method of claim 6 or 7.

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