Lithium sulfonate-based polyether single-ion polymer electrolyte DEBS-Li, and preparation method and application thereof

Abstract

The application discloses a lithium sulfonate-based polyether single-ion polymer electrolyte DEBS-Li and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. A lithium sulfonate-based polyether single-ion polymer nanofiber electrolyte with a three-dimensional network structure is prepared through a nucleophilic substitution reaction and an electrospinning method. The lithium sulfonate-based polyether single-ion polymer nanofiber electrolyte is used as a polymer electrolyte and has excellent comprehensive performance. After 500 6C charge-discharge cycles, the battery based on the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte has a discharge specific capacity that only decreases to 100.0 mAh / g, a capacity retention rate as high as 92.9%, and a coulombic efficiency that is basically always higher than 95%. Even at a high rate of 10C, after 1000 charge-discharge cycles, the battery with a PP film as the electrolyte has a discharge specific capacity that decreases to 53.7 mAh / g; in comparison, the battery with the es-DEBS-Li / 1M LiPF6 in EC / DMC still has a discharge specific capacity of 61.6 mAh / g, which is higher than that of the PP film.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium sulfonate-based polyether single-ion polymer electrolyte DEBS-Li, its preparation method and application, particularly its application in the preparation of porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membranes. Background Technology

[0002] The structural design of single-ion conductive polymer electrolytes can meet the high energy density and high safety requirements of lithium metal batteries (LMBs). Molecular structure engineering polymers can combine the advantages of two or more polymers while eliminating the individual disadvantages. For example, copolymers with ordered supramolecular structures formed by copolymerizing two or more different monomers effectively combine the advantages of polymers with different properties. One of the monomers acts as an ion conductor, while the copolymerized portion imparts other desired properties to the electrolyte, such as good mechanical strength and electrochemical stability. Therefore, molecular structure engineering can achieve significant ionic conductivity without sacrificing other properties of the polymer electrolyte (mechanical strength and electrochemical stability). Typical polymer molecular structures include: cross-linked polymers, copolymers, block polymers, comb polymers, branched polymers, and blends.

[0003] Lithium sulfonate structures are relatively common and have moderate polarity, making the design and preparation of corresponding single-ion polymer electrolytes relatively simple. However, lithium sulfonate has only one sulfone group on its oxygen negative charge that attracts electrons to disperse the negative charge electron cloud density, resulting in a relatively large delocalization energy of the anion in lithium sulfonate-type single-ion conductors, which is unfavorable for the solvation and dissociation of lithium ions. Polymer electrolytes with polar groups (such as ether, ester, nitrile, and fluorine groups) achieve lithium ion dissociation and dissociation through dissociation-coordination interactions during polymer chain rotation and vibration. + Transport. Polyether-based polymer electrolytes can form a stable SEI at the lithium metal / electrolyte interface, hindering continuous interfacial reactions and effectively stabilizing Li metal. Furthermore, the ethylene oxide (EO) units of the polyether possess a large amount of Li... + Donor and flexible chain mobility are beneficial for enhancing Li + Transport. Replacing hydrogen atoms in side-chain lithium sulfonates with fluorine atoms to prepare perfluorosulfonates can further improve their ionic conductivity. However, perfluorosulfonates face challenges such as complex synthetic routes and high costs. Chen et al., using LiPACA and LiPHFE as examples, demonstrated that polyarylene ethers are superior to polyamides in terms of polymer backbone as gel-type single-ion conductive electrolyte membranes. The structural differences between the two macromolecules are the reason for the observed morphological and electrochemical differences. Furthermore, the ether segments in polyarylene ethers can effectively promote ion conduction through strong electrostatic interactions with lithium ions in the polymer matrix.

[0004] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0005] Based on the above reasons, and addressing the problems or defects existing in the prior art, the purpose of this invention is to provide a lithium sulfonate-based polyether mono-ion polymer electrolyte (DEBS-Li), its preparation method, and its applications, solving or at least partially solving the aforementioned technical defects in the prior art. In this invention, a three-dimensional network structure of lithium sulfonate-based polyether mono-ion polymer nanofiber electrolyte is prepared through nucleophilic substitution reaction and electrospinning. As a polymer electrolyte, it exhibits excellent comprehensive performance.

[0006] To achieve the first objective of this invention, the technical solution adopted by this invention is as follows:

[0007] A lithium sulfonate-based polyether mono-ionic polymer electrolyte, DEBS-Li, is obtained through a nucleophilic substitution reaction of potassium dihydroxybenzenesulfonate (DHBS-K) with dichloroethyl ether (DCE).

[0008] The preparation method of the lithium sulfonate-based polyether single-ion polymer electrolyte DEBS-Li described above specifically includes the following steps:

[0009] Potassium dihydroxybenzenesulfonate, dichloroethyl ether, and potassium carbonate were added sequentially to a double-necked flask equipped with a water separator according to the formula. Then, dimethyl sulfoxide (DMSO) and toluene were added sequentially according to the formula. The resulting reaction mixture was heated to 155-165℃ and refluxed for 2-4 hours under inert gas protection, and then the temperature was slowly increased to 175-185℃ and refluxed for another 10-14 hours.

[0010] After the reaction is complete, the mixture is cooled, a precipitate is formed, filtered, washed, dried, lithiated, filtered again, and the resulting filtrate is dialyzed and then rotary evaporated. Finally, it is dried to obtain the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li.

[0011] Furthermore, in the above technical solution, the molar ratio of potassium dihydroxybenzenesulfonate to dichloroethyl ether is 1:1.

[0012] Furthermore, in the above technical solution, the molar ratio of potassium dihydroxybenzenesulfonate to potassium carbonate is 1:2.

[0013] Furthermore, in a preferred embodiment of the present invention, the ratio of potassium dihydroxybenzenesulfonate to dimethyl sulfoxide is 2 mmol: 3 mL.

[0014] Furthermore, in a preferred embodiment of the present invention, the ratio of potassium dihydroxybenzenesulfonate to toluene is 5 mmol: 4 mL.

[0015] Furthermore, in the above technical solution, the inert gas is preferably argon.

[0016] Furthermore, in the above technical solution, the reaction is preferably first refluxed at 160°C for 3 hours, and then slowly heated to 180°C for 12 hours.

[0017] Furthermore, in a preferred embodiment of the present invention, the dialysis time is 72 hours.

[0018] A second objective of this invention is to provide a lithium sulfonate-based polyether mono-ion polymer electrolyte, DEBS-Li, prepared by the method described above.

[0019] A third objective of this invention is to provide the application of the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li prepared by the above-described method in the preparation of porous lithium sulfonate-based polyether mono-ion nanofiber polymer electrolyte membranes.

[0020] A porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membrane (es-DEBS-Li nanofiber membrane) is prepared by electrospinning, comprising the following steps:

[0021] The lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li was mixed with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) according to the specified ratio, and then dissolved in dimethyl sulfoxide (DMSO) to form a homogeneous solution. The resulting solution was then spun into a film and dried to obtain the es-DEBS-Li nanofiber membrane.

[0022] Furthermore, in the above technical solution, the mass ratio of the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li to polyvinylidene fluoride-hexafluoropropylene is 1:2.

[0023] Furthermore, in the above technical solution, the mass fraction of the homogenized solution is 15-20%.

[0024] A fourth objective of this invention is to provide a porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membrane prepared by the method described above.

[0025] The fifth objective of this invention is to provide the application of the above-described porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membrane in lithium-ion batteries.

[0026] A lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator is the porous lithium sulfonate-based polyether mono-ion nanofiber polymer electrolyte membrane described above.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention prepares a three-dimensional network structure of lithium sulfonate-based polyether mono-ion polymer nanofiber electrolyte via nucleophilic substitution reaction and electrospinning. As a polymer electrolyte, it exhibits excellent comprehensive performance. The battery based on the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte of this invention, after 500 6C charge-discharge cycles, shows a discharge specific capacity decrease to only 100.0 mAh / g, achieving a capacity retention rate as high as 92.9%. Figure 9 c) and the coulombic efficiency is consistently above 95%. Even at a high rate of 10C, after 1000 charge-discharge cycles, the discharge specific capacity of the battery with PP film as electrolyte drops to 53.7 mAh / g; in contrast, the battery with es-DEBS-Li / 1M LiPF6 in EC / DMC still maintains a higher discharge specific capacity of 61.6 mAh / g than that of the PP film. Attached Figure Description

[0029] 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.

[0030] Figure 1 This is a schematic diagram illustrating the synthesis of DEBS-Li and es-DEBS-Li polymer nanofiber membranes in Example 1 and Application Example 1.

[0031] Figure 2 (a) NMR spectrum of DEBS-Li; (b) Infrared spectrum;

[0032] Figure 3 SEM images of es-DEBS-Li films prepared in Application Example 1 at different magnifications: (a) 5000, (b) 10000, (c) 40000; SEM images of PP films at different magnifications: (d) 10000, (e) 50000; (f) SEM images of es-DEBS-Li nanofibers and corresponding EDX elemental mapping images; (g) C element, (h) O element, (i) S element;

[0033] Figure 4 Contact angle with commercial electrolyte: (a) PP membrane after 10 s, (b) PP membrane after 120 s; (c) es-DEBS-Li membrane after 3 s, (d) es-DEBS-Li membrane after 12 s; Thermal stability of PP membrane and es-DEBS-Li membrane: (e) TG curve, (f) DSC curve;

[0034] Figure 5 Comparison of electrochemical performance of membranes in commercial electrolytes: (a) linear sweep voltammetry curves; (b) ionic conductivity; (c) corresponding impedance diagrams; time-current curves of impedance diagrams before and after insertion polarization in commercial electrolytes: (d) PP membrane, (e) PVDF-HFP membrane, (f) es-DEBS-Li membrane.

[0035] Figure 6 Figures showing the results of constant current cycling tests on lithium symmetric batteries with different electrolytes;

[0036] Figure 7 The morphology of the original lithium sheet, the lithium symmetric cells corresponding to PP and es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte after long-term constant current testing: (ac) optical photograph, (df) planar image, (gi) cross-section.

[0037] Figure 8 Cycling performance of Li / LiFePO4 batteries assembled with es-DEBS-Li-s electrolyte at room temperature at 0.1C;

[0038] Figure 9 Comparison of electrochemical performance of Li / LiFePO4 batteries assembled with es-DEBS-Li membrane and PP membrane in 1M LiPF6 in EC / DMC electrolyte system at room temperature: (a) rate performance; (b) charge-discharge curves of es-DEBS-Li electrolyte at different rates; (c) long-term cycling performance of es-DEBS-Li electrolyte at 6C; (d) long-term cycling performance at 10C. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Example 1

[0043] The preparation method of the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li according to this embodiment includes the following steps:

[0044] The monoionic polymer was obtained via a nucleophilic substitution reaction of potassium dihydroxybenzenesulfonate (DHBS-K) with dichloroethyl ether (DCE). The synthetic route is as follows: Figure 1 As shown: 4.664 g (20 mmol) of potassium dihydroxybenzenesulfonate, 2.889 g (20 mmol) of dichloroethyl ether, and 5.5284 g (40 mmol) of potassium carbonate were introduced into a double-necked flask equipped with a Dean-Stark water separator. 30 mL of dimethyl sulfoxide (DMSO) was added as solvent, and 16 mL of toluene as azeotropic agent. The reaction mixture was heated to 160 °C and refluxed for 3 h under argon protection, then slowly heated to 180 °C and reacted for 12 h. After the reaction was complete and cooled, a precipitate was formed in anhydrous ethanol, filtered, and washed with anhydrous ethanol. After drying, the product was dissolved in water, and an equimolar amount of lithium perchlorate was added and allowed to stand for 24 h. The lithium perchlorate was then removed by filtration. The filtrate was dialyzed for 72 h, and most of the solvent was removed by rotary evaporation. Finally, the product was dried to obtain the target product, named DEBS-Li.

[0045] Application Example 1

[0046] This application example describes a method for preparing an es-DEBS-Li nanofiber membrane, which includes the following steps:

[0047] like Figure 1 As shown, this experiment uses electrospinning to prepare nanofiber membranes. Specifically, after preliminary trials with different proportions, the polymer lithium salt product DEBS-Li obtained in Example 1 was dissolved in a certain amount of DMSO solvent at a mass ratio of 1:2 to prepare a homogeneous solution with a mass ratio of 15%. Then, the solution was spun into a membrane with a receiving distance of 15 cm, a voltage of 29 kV, and a spray rate of 4 μL / min. After drying at 60 °C for 12 h, it was cut into membranes with a diameter of 19 mm and then dried in a vacuum oven at 80 °C for 24 h. Finally, the obtained electrolyte membrane (named es-DEBS-Li) was placed in an argon-filled glove box for later use.

[0048] Comparative Application Example 1

[0049] The method for preparing a pure PVDF-HFP spun film in this comparative application example is basically the same as that in application example 1, except that the polymer lithium salt product DEBS-Li obtained in example 1 was not used in this comparative application example.

[0050] DEBS-Li electrolyte structure characterization

[0051] The 1H NMR spectrum of DEBS-Li synthesized in Example 1 ( 1 HNMR) such as Figure 2 As shown in Figure a, peak ad (3.5-4.5 ppm) is the proton peak on the ether chain, and peak eg (6.5-7.5 ppm) is the proton peak on the benzene ring; and by integration, the area ratio of the two integral parts is 2.67:1.00, indicating successful polymerization. To further verify this, based on the FTIR spectrum... Figure 2 b, Raw material DHBS-K with a wavenumber of 3300cm -1 The phenolic hydroxyl peaks near the site disappeared after polymerization; the wavenumber was 1517 cm⁻¹. -1 and 1447cm -1 The infrared absorption peak at this point belongs to the stretching vibration peak of CH on the benzene ring; the wavenumber is 1083 cm⁻¹. -1 and 1023cm -1 The peaks at these locations belong to the symmetric stretching vibration peaks of -SO2-. For DCE, the wavenumber is 2962 cm⁻¹. -1 and 2862cm -1 The infrared absorption peak at this point belongs to the stretching vibration peak of CH, with a wavenumber of 1120 cm⁻¹. -1 The absorption peak at this point belongs to the stretching vibration peak of the ether bond (COC), with a wavenumber of 745 cm⁻¹. -1 The absorption peak at that location belongs to the stretching vibration peak of C-Cl. For the polymerized DEBS-K, the wavenumber is 2924 cm⁻¹. -1 The infrared absorption peak at this location belongs to the stretching vibration peak of CH; the wavenumber is 1486 cm⁻¹. -1 The infrared absorption peak at this point belongs to the stretching vibration peak of CH on the benzene ring; the wavenumber is 1059 cm⁻¹. -1 and 1023cm -1 The peaks at these locations belong to the symmetric stretching vibration peaks of -SO2-; meanwhile, DEBS-K at 1125 cm⁻¹... -1 The formation of ether bonds (COC) further confirms the successful polymerization.

[0052] Meanwhile, gel permeation chromatography (GPC) analysis revealed polymers with a normally distributed degree of polymerization. Higher molecular weight allows for more ether-oxygen bonds, which facilitates ion transport. The results are shown in Table 1. The polydispersity index (M...)... w / M n The value of 1.18 confirms the success of the aggregation.

[0053] Table 1 Gel permeation chromatography

[0054]

[0055] Morphological characterization of nanofiber membranes

[0056] Scanning electron microscope (SEM) images of spun fiber membranes (es-DEBS-Li) and commercial PP membranes, as shown below. Figure 3 As shown, the es-DEBS-Li film exhibits highly open pores interconnected by nanofibers with diameters ranging from 100-150 nm and an average diameter of approximately 130 nm. Figure 3 Long fibers provide a continuous path for ion transport; the interlacing of the fibers creates a three-dimensional network structure, which offers higher wettability. A polymer network with a well-defined 3D structure can lead to phase separation of internal ions, forming a hierarchical structure conducive to ion movement and thus better facilitating electrolyte absorption. However, commercial PP films produced using the stretching method also show that their pore size is not completely uniform. Figure 3 (d and 3e). Therefore, thanks to the electrospinning process, es-DEBS-Li has high porosity and high electrolyte absorption rate, which are much higher than PP membranes, and also higher than most porous membranes prepared by casting, pore-forming agent methods, non-solvent-induced phase separation and other methods.

[0057] Highly continuous lithium-ion transport channels play a crucial role in enhancing lithium mobility in polymer electrolytes. SEM images and corresponding EDX elemental mapping images of the es-DEBS-Li film are shown. Figure 3 fi) indicates the uniform dispersion of these elements, among which sulfur comes from sulfonate groups, which can to some extent explain the uniform distribution of lithium ions in the es-DEBS-Li film. This is beneficial for achieving a uniform electroplating / stripping process of lithium ions and helps to suppress the growth of lithium dendrites.

[0058] Wetting and thermal stability tests

[0059] The wetting angle was measured using a wetting angle meter, and the reading was taken directly from the instrument. Thermogravimetric analysis was used to analyze the thermal stability of the material; the test atmosphere was nitrogen, and the heating rate was set to 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.

[0060] Good wettability facilitates the affinity between the separator and the electrolyte, expanding the contact area between them and thus increasing interfacial compatibility, which is beneficial for improving the electrochemical performance of the battery. The wettability to the electrolyte is characterized by dynamic contact angle testing. The adsorption of electrolyte by the es-DEBS-Li membrane and commercial PP membrane can be compared from the following perspectives: Figure 4 The difference is evident in the data: the es-DEBS-Li membrane achieves complete wetting with a contact angle of 0° at 12 seconds; while the PP membrane only decreases its contact angle by 14.1% within 120 seconds, still reaching a high of 55.9°. The highly polar sulfonic acid groups in the es-DEBS-Li membrane have a positive influence on this.

[0061] Combination Figure 4 Based on the thermogravimetric (TG) and differential scanning calorimetry (DSC) curves of ef, both the PP film and the pure PVDF-HFP spun film exhibit endothermic peaks corresponding to their melting points at 160.5℃ and 154.2℃, respectively. This indicates that the separator begins to melt at these temperatures due to its relatively low melting point, potentially leading to a short circuit due to contact between the positive and negative electrodes of the battery. Although es-DEBS-Li begins to experience mass loss around 300℃, the melting peak of DEBS-Li in the DSC curve appears at a relatively high 200.5℃, which is sufficient for practical applications.

[0062] Electrochemical performance testing

[0063] First, the electrochemical performance of several electrolytes was characterized by the electrochemical stability window (ESW), ionic conductivity, and transference number. Comparison shows that the electrochemical stability window of the PVDF-HFP / 1M LiPF6 in EC / DMC electrolyte is around 4.0V; at room temperature, the ionic conductivity of the PVDF-HFP / 1M LiPF6 in EC / DMC system is close to that of the PP film, but lower than that of the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte within the test temperature range (25℃-80℃); the lithium-ion transference number (t) of its corresponding lithium symmetric cell was obtained using the steady-state current method. Li + The value is only 0.23; in summary, it can be found that the PVDF-HFP / 1MLiPF6 in EC / DMC electrolyte cannot well meet the high requirements of batteries in actual operation. Therefore, the performance of the pure PVDF-HFP spun film system will not be explored further in the following content.

[0064] The electrolyte's ESW (Electrochemical Swing) can determine the battery's cycle life and safety. An ideal electrolyte exhibits excellent stability over a wide operating voltage range and is redox inert to both the anode and cathode. ESW depends not only on the electrolyte's composition but also on its compatibility with the electrodes.

[0065] EIS testing was performed on Li / LFP cells 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 assembled Li / SS (stainless steel spacer) cells. The LSV testing 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.

[0066] The electrochemical windows of several electrolytes were tested using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. The results are as follows: Figure 5 As can be seen from graph a, the ESW of both PP / 1M LiPF6 in EC / DMC and PVDF-HFP / 1M LiPF6 in EC / DMC is lower than that of es-DEBS-Li electrolyte. The graph shows that the oxidation peak of es-DEBS-Li electrolyte occurs around 4.23V, indicating that this polymer electrolyte is electrochemically inert in the 2.5V-4.2V voltage range and can be used in lithium batteries. Figure 5 As shown in b, the ionic conductivity of several electrolytes increases with increasing temperature. Within the tested temperature range, the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte exhibits the highest conductivity, exceeding that of the PP membrane or pure PVDF-HFP electrolyte. This indirectly verifies that the presence of lithium sulfonate-based polyether single ions can improve conductivity to some extent. It is noteworthy that the conductivity of the es-DEBS-Li-s (es-DEBS-Li︱EC / DMC single ion system) electrolyte is too low throughout the entire tested temperature range, limiting its application as a single-ion conductive polymer electrolyte. The impedance spectra of the three electrolytes are shown below. Figure 5 As shown in Figure c, the es-DEBS-Li-s battery exhibits the highest interfacial resistance. However, the interfacial resistance decreases after the addition of a commercial electrolyte. The introduction of the small-molecule lithium salt LiPF6 into the commercial electrolyte improves the interface, which is related to... Figure 5 The conductivity in b is consistent with this. High ionic conductivity and good electrode-polymer electrolyte interfacial compatibility play a crucial role in improving battery performance.

[0067] At room temperature, the te of PP / 1M LiPF6in EC / DMC, PVDF-HFP / 1M LiPF6in EC / DMC, and es-DEBS-Li / 1M LiPF6in EC / DMC electrolytes on lithium symmetric cells was measured using the steady-state current method. Li + The impedance spectrum and time-varying current response of DC polarization are as follows: Figure 5As shown in df, detailed test values ​​are summarized in Table 2 below. The t values ​​for PP / 1M LiPF6inEC / DMC and PVDF-HFP / 1M LiPF6inEC / DMC are... Li + They are 0.27 and 0.23 respectively. Figure 5 d and Figure 5 e), this is due to PF6 - This is caused by the high mobility of anions. The t of the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte... Li + The value of 0.62 is significantly higher than that of commercial electrolyte systems, indicating that the single-ion polymer electrolyte improves the t Li + The function ( Figure 5 f), -SO3 - Anchoring anions to the polymer backbone restricts their migration, and this approach effectively increases the lithium-ion transference number in the electrolyte.

[0068] Table 2. Measured values ​​of the corresponding lithium-ion transference numbers.

[0069]

[0070] Investigating t through peeling / electroplating cycle tests Li + The effect of commercial PP film on lithium dendrite growth on lithium metal anodes, and the lithium symmetric cell assembled with es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte at 1.5 mA / cm 2 Long-term constant current cycling test at current density, such as Figure 6 As shown. This experiment was conducted on the LAND test system, assembling a Li|film|Li battery with a current density of 2.5 mA / cm². -2 / 0.05mAcm -2 The stripping and electroplating times were both 1 hour. For es-DEBS-Li / 1M LiPF6 in EC / DMC, due to its t Li + The high polarization voltage allows for the observation of a fairly stable and small polarization voltage, which is beneficial for suppressing lithium dendrite growth. In contrast, commercial PP membrane electrolytes remain unstable throughout the test period, and their Li / Li symmetric cells exhibit a large amount of lithium dendrite growth and dead lithium accumulation on the surface after cycling, leading to increased polarization.

[0071] The microstructure of the separator was characterized using field emission scanning electron microscopy (FESEM). The gold sputtering time was 60 s. Prior to testing, the separator was vacuum-dried at 80 °C for 24 h. The battery, after long-term constant current cycling testing, was disassembled, and the dendrite growth on the lithium anode surface was investigated using optical and SEM images. The results are as follows: Figure 7 As shown, the original lithium sheet surface is quite smooth and flat. However, the lithium sheet surface of the PP / 1M LiPF6 in EC / DMC electrolyte after constant current cycling is quite rough and uneven, with a large number of lithium dendrites and "dead lithium." The SEM cross-sectional image also shows severe volume expansion, likely due to the large deposition of "dead lithium." Compared to the PP film, the lithium anode surface of the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte is smoother, with less volume expansion, and it inhibits lithium dendrite growth. The "rigid-to-flexible" distribution strategy of benzenesulfonic acid and ether bonds on the polymer electrolyte effectively acts as a protective buffer layer to release internal stress, thereby extending the electrode's cycle life.

[0072] A preliminary study was conducted on the cycling performance of the es-DEBS-Li-s electrolyte (es-DEBS-Li︱EC / DMC single-ion system), such as... Figure 8As shown. This experiment was conducted on a LAND battery testing system, where Li / LFP batteries were assembled and charge-discharge tests were performed at different rates. The preparation process of the LiFePO4 positive electrode was as follows: a certain amount of active material (LiFePO4), acetylene black (AB) conductive additive, and PVDF binder in a mass ratio of 7:2:1 were weighed and dissolved in a calculated amount of N-methylpyrrolidone (NMP) to form a slurry, which was then cast onto aluminum foil using a coating machine. Subsequently, the coated aluminum foil was 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 coin cell, and transferred to a vacuum oven at 80°C for overnight drying. Coulombic efficiency (charge-discharge efficiency) is the percentage of the battery's discharge specific capacity to its charge specific capacity in the same cycle. Cyclic performance tests were conducted at a certain rate to evaluate the practical application of the electrolyte in high-performance lithium metal batteries. On the one hand, the poor dissociation of lithium sulfonate polymer electrolytes leads to lithium ion deficiency, reducing the number of lithium ions during charge and discharge, thus resulting in low coulombic efficiency (CE). On the other hand, during battery discharge, lithium metal deposits on the negative electrode detach and become trapped in the SEI layer. During this process, the lithium metal loses its connection to the positive electrode, thus losing its activity and no longer participating in battery cycling, generating a large amount of "inert lithium." These trapped "inert lithium" are a significant cause of low battery CE. Researchers also found that the more "inert lithium" formed, the lower the battery CE. Simultaneously, the amount of lithium ions in the SEI layer remains consistently low. This electrolyte is prone to overcharging at 0.1C, resulting in poor CE and inability to withstand long-term cycling. This is related to the high interfacial resistance of the es-DEBS-Li-s electrolyte and the aforementioned... Figure 5 The excessively low ionic conductivity in b is closely related to the fact that the high dissociation energy of lithium sulfonate-type single-ion conductive polymer electrolytes limits the dissociation of lithium ions.

[0073] Finally, the electrochemical performance of two electrolytes, es-DEBS-Li / 1M LiPF6 in EC / DMC and PP / 1M LiPF6 in EC / DMC, was further evaluated in Li / LiFePO4 batteries. This experiment was conducted on a LAND testing system. A LiFePO4|Li coin cell (model 2025) was constructed to evaluate the practical application of the separator as a high-performance lithium metal battery separator. Charge-discharge tests were first performed at different rates, with six cycles at each rate. Then, a suitable rate was selected for long-term cycle performance testing. The results are as follows: Figure 9As shown, the battery based on es-DEBS-Li / 1MLiPF6 in EC / DMC electrolyte exhibited reversible discharge capabilities of 150.7 mAh / g and 88.0 mAh / g at charge / discharge rates as low as 0.5C and as high as 10C, respectively, which are higher than the corresponding values ​​(149.4 mAh / g and 70.0 mAh / g) of the battery based on commercial PP / 1MLiPF6 in EC / DMC electrolyte. Figure 9 a). After 500 6C charge-discharge cycles, the battery based on es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte showed a discharge specific capacity decrease to only 100.0 mAh / g, achieving a capacity retention rate as high as 92.9%. Figure 9 c), and the coulombic efficiency is consistently above 95%. Even at a high rate of 10C, after 1000 charge-discharge cycles, the discharge specific capacity of the battery with PP film as electrolyte drops to 53.7 mAh / g; in contrast, the battery with es-DEBS-Li / 1M LiPF6 in EC / DMC still maintains a higher discharge specific capacity of 61.6 mAh / g than that of the PP film. Figure 9 d) Furthermore, its efficiency consistently exceeded that of the PP film throughout the entire cycle test. The high capacity of the battery is mainly attributed to its high ionic conductivity and low interfacial resistance. The addition of the commercial electrolyte LiPF6 improved the problem of excessively low ionic conductivity. The small molecule lithium salt may also have promoted the dissociation of lithium sulfonate in the single-ion polymer electrolyte. Therefore, the es-DEBS-Li / 1M LiPF6 in EC / DMC electrolyte can achieve excellent high-rate and long-cycle performance.

Claims

1. A method for preparing a lithium sulfonate-based polyether single-ion polymer electrolyte DEBS-Li, characterized in that: The method specifically includes the following steps: Potassium dihydroxybenzenesulfonate, dichloroethyl ether, and potassium carbonate were added sequentially to a double-necked flask equipped with a water separator according to the specified ratio. Then, dimethyl sulfoxide and toluene were added sequentially according to the specified ratio. The resulting reaction mixture was heated to 155-165°C under inert gas protection. o Reflux at C for 2-4 hours, then slowly increase the temperature to 175-185°C. o C continues the reflux reaction for 10-14 hours; After the reaction is complete, the mixture is cooled, a precipitate is formed, filtered, washed, dried, lithiated, filtered again, and the resulting filtrate is dialyzed and then rotary evaporated. Finally, it is dried to obtain the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li.

2. The method according to claim 1, characterized in that: The molar ratio of potassium dihydroxybenzenesulfonate to dichloroethyl ether is 1:

1.

3. The method according to claim 1, characterized in that: The molar ratio of potassium dihydroxybenzenesulfonate to potassium carbonate is 1:

2.

4. The lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li prepared by the method according to any one of claims 1-3.

5. The application of the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li prepared by the method according to any one of claims 1-3 in the preparation of porous lithium sulfonate-based polyether mono-ion nanofiber polymer electrolyte membranes.

6. A method for preparing a porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membrane, characterized in that: Includes the following steps: The lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li described in claim 4 is mixed with polyvinylidene fluoride-hexafluoropropylene according to the specified ratio, and then dissolved in dimethyl sulfoxide to form a homogeneous solution; the resulting solution is then spun into a film and dried to obtain the porous lithium sulfonate-based polyether mono-ion nanofiber polymer electrolyte membrane.

7. The method according to claim 6, characterized in that: The mass ratio of the lithium sulfonate-based polyether mono-ion polymer electrolyte DEBS-Li to polyvinylidene fluoride-hexafluoropropylene is 1:

2.

8. The porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membrane prepared by the method of claim 6 or 7.

9. The application of the porous lithium sulfonate-based polyether single-ion nanofiber polymer electrolyte membrane prepared by the method of claim 6 or 7 in lithium-ion batteries.

10. A lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator is a porous lithium sulfonate-based polyether mono-ion nanofiber polymer electrolyte membrane prepared by the method of claim 6 or 7.

Images