Composite solid polymer electrolyte for inhibiting growth of lithium dendrites as well as preparation method and application of composite solid polymer electrolyte

Abstract

The invention belongs to the technical field of new energy, and particularly discloses a composite solid polymer electrolyte for inhibiting growth of lithium dendrites and a preparation method and application thereof. According to the invention, boron-containing functional groups CDs (BCDs) which are highly compatible with common SPEs and have good affinity to TFSI anions in lithium bis (trifluoromethane sulfonimide) are synthesized by a simple and cheap method, and the BCDs (BCDs) are used as a filler to be introduced into a traditional polyoxyethylene electrolyte to prepare the composite SPEs. The composite SPEs have the following advantages: 1) the BCDs which are small in size and highly compatible with the PEO can enable the PEO to form a continuous amorphous region, so that a continuous rapid lithium ion transmission channel is formed, and the lithium ion conductivity is effectively improved; 2) the uniformly dispersed BCDs can effectively fix TFSI anions based on a B-containing functional group, and the LITN of the composite SPEs is effectively improved; and 3) the formation of lithium dendrites is effectively inhibited, and the overall performance of the LSBs is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy, and in particular relates to a composite solid polymer electrolyte for inhibiting the growth of lithium dendrites, and a preparation method and application thereof. Background Art

[0002] Lithium-sulfur batteries (LSBs) have a high theoretical energy density (2600Wh Kg -1 ) has received widespread attention. However, the safety issues caused by the coexistence of lithium metal anodes (LMAs) and flammable liquid electrolytes (LEs) still restrict the practical application of LSBs. This is because LMAs are prone to form overgrown lithium dendrites during the cycle process. These dendrites may pierce the separator and cause the battery to short-circuit, and release a large amount of heat, which in turn causes the flammable LEs to catch fire or even explode. At the same time, the sulfur positive electrode and the commonly used lithium-ion battery negative electrode both need to obtain lithium ions during the discharge process and cannot be used together, which also makes LMA difficult to replace in LSBs. Therefore, developing non-flammable solid electrolytes to replace LEs is an effective solution to the safety problems of LSBs.

[0003] Compared with inorganic solid electrolytes, solid polymer electrolytes (SPEs) have the advantages of light weight, strong plasticity, good flexibility, simple preparation process, and easier to form a stable interface with the electrode, and have attracted widespread attention from researchers. Although non-flammable SPEs can solve the safety problem caused by lithium dendrites, they cannot inhibit the formation of lithium dendrites, and the adverse effects on the performance of LSBs still exist, which are mainly caused by the following two reasons: First, the uneven distribution of lithium ions in SPEs can easily lead to uneven deposition of lithium ions and form lithium dendrites; second, the passivation film formed by the spontaneous reaction of SPEs and LMA does not have sufficient mechanical properties and is easily punctured by lithium dendrites.

[0004] To solve this problem, the researchers designed a plan to further improve SPEs, including optimizing the interface between SPE and LMA. Specifically, the interface between SPEs and LMA is modified to have sufficient mechanical properties to inhibit the formation of lithium dendrites; or, the lithium ion transfer number (LITN) of SPEs is increased. The uneven ion distribution in SPEs is mainly caused by the simultaneous migration of anions and cations. The molecular chains of commonly used SPEs are closely related to Li +The high degree of interaction causes its transfer speed to be slower than that of anions, and the LITN is low, which seriously affects the distribution of lithium ions therein. Therefore, inhibiting the movement of anions and improving the LITN of SPEs are also effective strategies to inhibit the formation of lithium dendrites. Chinese patent CN106129469B (Central South University) discloses a composite solid polymer electrolyte, including a polymer, carbon quantum dots, an organic lithium salt or an organic sodium salt, wherein the polymer is selected from polyethylene oxide, polyacrylonitrile or polymethyl methacrylate polymer, the organic lithium salt is selected from lithium perchlorate, lithium trifluoromethanesulfonate or lithium bistrifluoromethanesulfonyl imide, and the organic sodium salt is selected from sodium perchlorate, sodium trifluoromethanesulfonate or sodium bistrifluoromethanesulfonyl imide. This patent composites carbon quantum dots with polymers and organic lithium / sodium salts, wherein the carbon quantum dots are small in size and have good dispersibility, and can be evenly dispersed in the polymer, which can effectively reduce the crystallinity of the polymer matrix in the electrolyte. At the same time, because the carbon quantum dots can interact with the organic lithium / sodium salts, their dissociation rate is increased, thereby enhancing the ion conductivity of the polymer electrolyte. However, there is still room for further improvement in the performance of this composite solid polymer electrolyte. Summary of the invention

[0005] The main technical problem solved by the present invention is to provide a composite solid polymer electrolyte for inhibiting the growth of lithium dendrites, effectively inhibiting the formation of lithium dendrites and improving the electrochemical performance of lithium-sulfur batteries (LSBs).

[0006] Secondly, the present invention provides a method for preparing the composite solid polymer electrolyte.

[0007] Thirdly, the present invention provides an application of the composite solid polymer electrolyte in the preparation of a lithium-sulfur battery.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] A composite solid polymer electrolyte for inhibiting the growth of lithium dendrites. The preparation raw materials include: high molecular polymer, boron-doped carbon quantum dots and organic lithium salt.

[0010] As a preferred embodiment of the present invention, the high molecular polymer is selected from one or more of polyethylene oxide (PEO), polyvinyl chloride (PVC), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and the like.

[0011] Specifically, the weight average molecular weight (Mw) of the high molecular weight polymer is 100,000-2,000,000.

[0012] As a preferred embodiment of the present invention, the size of the boron-doped carbon quantum dots is ≤20 nm, and more preferably ≤5 nm.

[0013] Specifically, the boron content in the boron-doped carbon quantum dots is 5-8 atomic %.

[0014] Specifically, the boron-doped carbon quantum dots contain at least elements such as B, N, C, and O.

[0015] As a preferred embodiment of the present invention, the organic lithium salt is selected from one or more of lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiOTF), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) and the like.

[0016] As a preferred embodiment of the present invention, the mass ratio of the high molecular polymer to the boron-doped carbon quantum dots is 10-15:1.

[0017] As a preferred embodiment of the present invention, the molar ratio of the high molecular polymer to the organic lithium salt is 10-20:1.

[0018] As a preferred embodiment of the present invention, the raw materials for preparing the composite solid polymer electrolyte include: polyethylene oxide (PEO), boron-doped carbon quantum dots and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI);

[0019] The mass ratio of the polyethylene oxide to the boron-doped carbon quantum dots is 13:1;

[0020] The molar ratio of the polyethylene oxide to lithium bis(trifluoromethanesulfonyl)imide is 15:1.

[0021] A method for preparing a composite solid polymer electrolyte for inhibiting lithium dendrite growth comprises the following steps:

[0022] The high molecular polymer, boron-doped carbon quantum dots, organic lithium salt and organic solvent are uniformly mixed, formed and then dried to obtain a composite solid polymer electrolyte.

[0023] As a preferred embodiment of the present invention, the method for preparing the boron-doped carbon quantum dots is as follows: using 3-aminophenylborate hydrochloride as a raw material, and adopting a hydrothermal synthesis method to prepare the boron-doped carbon quantum dots.

[0024] Specifically, the method for preparing boron-doped carbon quantum dots comprises the following steps:

[0025] Dissolve 3-aminophenylborate hydrochloride in water to obtain a solution, transfer the solution to a reactor, and use a bottom-up hydrothermal synthesis method to perform a hydrothermal reaction at 180-220° C. for 6-10 hours. After the reaction is completed, cool to room temperature and dry to obtain boron-doped carbon quantum dots.

[0026] As a preferred embodiment of the present invention, the organic solvent is selected from one or more of acetonitrile (ACN), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. More preferably, it is acetonitrile.

[0027] A composite solid polymer electrolyte for inhibiting lithium dendrite growth and its application in preparing lithium-sulfur batteries (LSBs).

[0028] Beneficial effects of the present invention:

[0029] The composite solid polymer electrolyte for inhibiting the growth of lithium dendrites provided by the present invention has the main improvement of using boron-doped carbon quantum dots (BCDs). As is well known, carbon quantum dots (CDs) have a small-sized (3-5nm) carbon core and easily controllable external functional groups, which make them have both organic and inorganic properties, and are very suitable for use as nanofillers to improve the performance of SPEs. The present invention introduces boron-doped carbon quantum dots into the solid polymer electrolyte by doping carbon quantum dots with boron and utilizing the property of fixing organic lithium salt anions with B functional groups, thereby increasing the LITN of SPEs and improving the lithium ion conductivity of the composite SPEs.

[0030] The present invention synthesizes boron-containing functional group CDs (BCDs) that are highly compatible with commonly used SPEs and have good affinity for TFSI anions in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) by a simple and inexpensive method, and introduces them into a traditional polyethylene oxide (PEO) electrolyte as a filler to prepare composite SPEs. In the composite SPEs: 1) small-sized BCDs are highly compatible with PEO, so that they are uniformly dispersed in PEO; 2) uniformly distributed BCDs with carbon cores form continuous amorphous regions in PEO, thereby forming continuous and fast lithium ion transmission channels, effectively improving the lithium ion conductivity of the composite SPEs; 3) the uniformly dispersed BCDs can effectively fix TFSI anions based on their B-containing functional groups, which can effectively improve the LITN of the composite SPEs. Therefore, the composite solid polymer electrolyte provided by the present invention can effectively inhibit the formation of lithium dendrites and improve the overall performance of lithium-sulfur batteries (LSBs). BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Scanning electron microscope (SEM) images of PEO-BCDs, PEO-CDs and PEO-LiTFSI in the experimental example.

[0032] Figure 2 Characterization diagrams of PEO-BCDs, PEO-CDs and PEO-LiTFSI in the experimental examples: a) XRD; b) DSC diagram.

[0033] Figure 3 Arrhenius plot of the ionic conductivity of PEO-BCDs, PEO-CDs and PEO-LiTFSI in the experimental example.

[0034] Figure 4 These are the chronoamperometric curves and AC impedance spectra of the lithium symmetric batteries assembled with PEO-BCDs, PEO-CDs and PEO-LiTFSI before and after polarization in the experimental example.

[0035] Figure 5 This is the voltage-time comparison diagram of the lithium symmetric battery assembled with PEO-BCDs, PEO-CDs and PEO-LiTFSI at different current densities in the experimental example.

[0036] Figure 6 The lithium symmetric battery assembled with PEO-BCDs, PEO-CDs and PEO-LiTFSI in the experimental example is 0.05 mA cm -2 Cycling performance diagram at different current densities.

[0037] Figure 7 This is the SEM image of the lithium symmetric battery assembled with PEO-BCDs, PEO-CDs and PEO-LiTFSI after cycling in the experimental example.

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the above drawings obtained in the experimental examples are briefly introduced. It should be understood that the above drawings only show some experimental examples of the present invention and should not be regarded as any limitation on the scope of protection of the claims. For ordinary technicians in this field, other related drawings can also be obtained based on these drawings without creative work. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments and experimental examples. However, it should be understood by those skilled in the art that the embodiments are only used to illustrate the technical solution of the present invention and should not be regarded as limiting the scope of protection of the present invention. Based on the following embodiments, all other implementation schemes obtained by ordinary technicians in the field without making creative work, such as modification, deformation or simple replacement, should belong to the scope of protection of the present invention.

[0040] Unless otherwise specified, the experimental methods used in the following embodiments and experimental examples are all conventional methods; the raw materials (including biological materials), reagents, culture media, instruments, etc. used are all commonly used in the art, available to the public or commercially available unless otherwise specified; the terms and abbreviations involved have the conventional meanings in the art, such as PBS buffer is phosphate buffered saline.

[0041] Example

[0042] This embodiment provides a composite solid polymer electrolyte for inhibiting the growth of lithium dendrites. The raw materials for preparation include: polyethylene oxide (PEO), boron-doped carbon quantum dots and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The preparation method includes the following steps:

[0043] 1) Preparation of BCDs: BCDs were prepared by bottom-up hydrothermal synthesis. 0.5 g of 3-aminophenylborate hydrochloride was dissolved in 50 mL of deionized water, and the solution was transferred to a 100 mL polytetrafluoroethylene-lined reactor. After being hydrothermally heated at 200°C for 8 h in a forced air drying oven, the solution was naturally cooled to room temperature, and the obtained solution was subjected to rotary evaporation. After freeze drying, the sample was collected to obtain BCDs. For analysis and characterization, see patent application CN115602811A.

[0044] 2) Preparation of SPEs: PEO and LiTFSI were prepared into polymer electrolyte slurry at a set molar ratio of 15:1. 0.6 g PEO (Mw = 1000000) and 0.2610 g lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were dissolved in 8 mL acetonitrile solvent, magnetically stirred and then 0.04532 g BCDs were added, and then stirred for 12 h; the slurry was cast on a polytetrafluoroethylene plate and cooled naturally for 48 h to obtain PEO-BCDs.

[0045] All the above preparation steps were completed in a glove box filled with argon.

[0046] This embodiment also provides an application of a composite solid polymer electrolyte for inhibiting the growth of lithium dendrites in the preparation of lithium-sulfur batteries (LSBs). Specifically, a CR2025 button battery shell is used to assemble a lithium sheet, PEO-BCDs, a lithium sheet, a gasket, a spring, and a battery negative electrode shell together in sequence, and the battery is sealed to obtain a Li||Li symmetrical battery.

[0047] In other embodiments of the present invention, the raw materials, types, dosage, etc. of the composite solid polymer electrolyte can be arbitrarily selected or taken within a given range without substantially affecting the overall performance of the composite SPEs.

[0048] Comparative Example 1

[0049] The composite solid polymer electrolyte provided in this comparative example is different from the above-mentioned embodiment in that the added filler is CDs, and the rest is the same as the embodiment. The all-solid polymer electrolyte prepared in comparative example 1 is recorded as PEO-CDs.

[0050] The preparation method of CDs in this comparative example is: CDs are prepared by a bottom-up hydrothermal synthesis method. First, 4.8 g of anhydrous citric acid is weighed and dissolved in 50 mL of deionized water, and then 1.675 mL of ethylenediamine is quickly added to the anhydrous citric acid solution with a pipette, and after stirring evenly, the mixed solution is transferred to a 100 mL polytetrafluoroethylene-lined reactor, and hydrothermally heated at 200°C for 5 hours and then naturally cooled to room temperature. The obtained solution is rotary evaporated and freeze-dried to obtain a dark red-brown powder sample, which is CDs. All the above preparation steps are completed in a glove box filled with argon.

[0051] Comparative Example 2

[0052] The solid polymer electrolyte provided in this comparative example is different from the above-mentioned embodiment in that BCDs is not added, and the rest is the same as the embodiment. The all-solid polymer electrolyte prepared in comparative example 2 is recorded as PEO-LiTFSI.

[0053] Experimental example

[0054] Experimental method: The solid polymer electrolytes prepared in the examples and comparative examples were subjected to transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis. Figure 1-2 shown.

[0055] Figure 1 The surface morphologies of the all-solid-state electrolyte membrane PEO-BCDs in the embodiment are compared with those of the all-solid-state electrolyte membrane PEO-CDs in comparative example 1 and the all-solid-state electrolyte membrane PEO-LiTFSI in comparative example 2. In comparison, the surface of PEO-BCDs is smoother and denser, which is beneficial to improving the interface contact between the electrolyte and the electrode.

[0056] Figure 2 The XRD and DSC of the all-solid electrolyte membrane PEO-BCDs in the embodiment were compared with the all-solid electrolyte membrane PEO-CDs in Comparative Example 1 and the all-solid electrolyte membrane PEO-LiTFSI in Comparative Example 2. The results show that PEO-BCDs and PEO-CDs have lower crystallinity and melting temperature, indicating that the more flexible the polymer chain in the PEO electrolyte, the more flexible the addition of BCDs and CDs can destroy the crystalline region, promote the movement of the chain segments, weaken the intermolecular interaction of the PEO chain, and lead to a decrease in the crystallinity of the polymer.

[0057] Experimental method: The solid polymer electrolytes prepared in the embodiment and the comparative example were respectively subjected to electrochemical impedance spectroscopy (EIS) test, and the formula was used: (Where σ is the ionic conductivity of the electrolyte (S cm -1 ), L is the thickness of the electrolyte membrane (cm), R is the bulk impedance of the electrolyte membrane (Ω), and S is the area of ​​the electrolyte membrane (cm2 )) to calculate the ionic conductivity of the solid electrolyte. EIS test conditions: using the CHI-760E workstation produced by Shanghai Chenhua Instrument Co., Ltd., the frequency range is set to 1.0MHz to 0.01Hz, the sine amplitude is 10mV, and the temperature range is 25℃ to 90℃. The experimental results are as follows Figure 3 shown.

[0058] Figure 3 The ionic conductivity of the all-solid electrolyte membrane PEO-BCDs in the embodiment is compared with that of the all-solid electrolyte membrane PEO-CDs in comparative example 1 and the all-solid electrolyte membrane PEO-LiTFSI in comparative example 2 at different temperatures. The results show that the ionic conductivity of PEO-BCDs is higher than that of PEO-CDs and PEO-LiTFSI.

[0059] Experimental method: The solid polymer electrolyte prepared in the embodiment and the comparative example was used to measure the ion migration number t of the electrolyte membrane by combining the constant potential DC polarization method and EIS test. Li + First, the electrolyte membrane is placed between symmetrical metal lithium sheets to assemble a Li|SPE|Li symmetric battery. Second, a small and stable polarization voltage (ΔV) is applied to the battery during the test, and the initial current (I0) and stable current (I S ). And measure the impedance before and after polarization, denoted as R0 and R S Test conditions: Use CHI-760E workstation produced by Shanghai Chenhua Instrument Co., Ltd., set the frequency range to 1.0MHz to 0.01Hz, set the polarization voltage to 10mV, and the polarization time to 10800 seconds. Calculate the ion migration number of the electrolyte membrane according to the formula: The experimental results are as follows Figure 4 shown.

[0060] Figure 4 The LITN of the all-solid electrolyte membrane PEO-BCDs in the embodiment is compared with the all-solid electrolyte membrane PEO-CDs in Comparative Example 1 and the all-solid electrolyte membrane PEO-LiTFSI in Comparative Example 2. It can be seen from the figure that the ion migration number of Li|PEO-LiTFSI|Li is only 0.11, the ion migration number of Li|PEO-CDs|Li is 0.29, and the ion migration number of Li|PEO-BCDs|Li is as high as 0.67.

[0061] Experimental method: The solid polymer electrolytes prepared in the embodiment and comparative example were used to assemble Li|SPE|Li symmetric batteries for constant current chronopotentiometry experiments, aiming to evaluate the deposition and precipitation behavior of metallic lithium in the solid electrolyte and the influence of interface stability on battery performance under specific conditions. Figure 5Test conditions: different current densities were set, 0.05 mA cm -2 , 0.1mA cm -2 , 0.25mA cm -2 , 0.5mA cm -2 , 1mA cm -2 , capacity density 0.5mAh cm -2 . Figure 6 Test conditions: current density 0.05mAcm -2 , capacity density 0.5mAh cm -2 The experimental results are as follows Figure 5-6 shown.

[0062] Figure 5 , Figure 6 The polarization curves of the all-solid electrolyte membrane PEO-BCDs in the embodiment, the all-solid electrolyte membrane PEO-CDs in comparative example 1, and the all-solid electrolyte membrane PEO-LiTFSI in comparative example 2 in Li||Li symmetric cells were compared. Figure 5 The comparison was conducted at different current densities, and the results showed that the Li||Li battery using PEO-BCDs has a smaller polarization voltage. Figure 6 The constant current charge and discharge test was performed with a current density of 0.05 mA cm -2 The results show that the Li||Li battery using PEO-BCDs has a smaller polarization voltage and a longer cycle life, indicating that the PEO-BCDs prepared in the embodiment have better cycle stability for metallic Li and good ability to inhibit lithium dendrites. Since the system contains more free lithium ions, this also provides more opportunities for the uniform deposition of lithium ions on the lithium negative electrode.

[0063] Experimental method: The lithium metal obtained from the solid polymer electrolyte assembled Li|SPE|Li symmetric battery prepared in the comparative example and the comparative example after cycling was subjected to scanning electron microscopy (SEM) analysis on its surface. Figure 7 shown.

[0064] Figure 7 The surface morphology of the all-solid electrolyte membrane PEO-BCDs in the embodiment after cycling in the Li||Li symmetric battery assembled with the all-solid electrolyte membrane PEO-CDs in Comparative Example 1 and the all-solid electrolyte membrane PEO-LiTFSI in Comparative Example 2 is compared. As can be seen from the figure, there are many dendrite-like protrusions on the surface of PEO-LiTFSI, and relatively few dendrite protrusions of PEO-CDs, while the surface of PEO-BCDs is smoother, indicating that the stripping / lithium plating process is uniform and a stable SEI layer is formed, which further confirms that PEO-BCDs has a good ability to inhibit lithium dendrites.

[0065] Although the technical solution of the present invention has been described in detail above with general descriptions, specific implementation methods and test examples, it should be noted that the embodiments and test examples are only used to illustrate the technical solution and technical effects of the present invention, and should not be regarded as any limitation on the protection scope of the present invention. Simple deformation, modification or improvement based on the technical concept of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A composite solid polymer electrolyte for inhibiting lithium dendrite growth, characterized in that: The raw materials for preparing the composite solid polymer electrolyte include: high molecular polymer, boron-doped carbon quantum dots and organic lithium salt.

2. The composite solid polymer electrolyte according to claim 1, characterized in that: The high molecular polymer is selected from one or more of polyethylene oxide, polyvinyl chloride, polyacrylonitrile and polymethyl methacrylate; And / or, the organic lithium salt is selected from one or more of lithium perchlorate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl imide).

3. The composite solid polymer electrolyte according to claim 1, characterized in that: The weight average molecular weight of the high molecular weight polymer is 100000-2000000; And / or, the size of the boron-doped carbon quantum dots is ≤20 nm; And / or, the boron content in the boron-doped carbon quantum dots is 5-8 atomic%.

4. The composite solid polymer electrolyte according to claim 1, characterized in that: The mass ratio of the high molecular polymer to the boron-doped carbon quantum dots is 10-15:1; And / or, the molar ratio of the high molecular polymer to the organic lithium salt is 10-20:

1.

5. The composite solid polymer electrolyte according to claim 3 or 4, characterized in that: The raw materials for preparing the composite solid polymer electrolyte include: polyethylene oxide, boron-doped carbon quantum dots and lithium bis(trifluoromethanesulfonyl)imide; The mass ratio of the polyethylene oxide to the boron-doped carbon quantum dots is 13:1; The molar ratio of the polyethylene oxide to lithium bis(trifluoromethanesulfonyl)imide is 15:

1.

6. A method for preparing a composite solid polymer electrolyte for inhibiting lithium dendrite growth as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: The high molecular polymer, boron-doped carbon quantum dots, organic lithium salt and organic solvent are uniformly mixed, formed and then dried to obtain a composite solid polymer electrolyte.

7. The preparation method according to claim 6, characterized in that: The method for preparing the boron-doped carbon quantum dots comprises: using 3-aminophenylborate hydrochloride as a raw material and adopting a hydrothermal synthesis method to prepare the boron-doped carbon quantum dots.

8. The preparation method according to claim 7, characterized in that: The method for preparing boron-doped carbon quantum dots comprises the following steps: Dissolve 3-aminophenylborate hydrochloride in water to obtain a solution; transfer the solution to a reactor, use a bottom-up hydrothermal synthesis method, perform a hydrothermal reaction at 180-220° C. for 6-10 hours, cool to room temperature after the reaction is completed, and dry to obtain boron-doped carbon quantum dots.

9. The preparation method according to claim 7, characterized in that: The organic solvent is selected from one or more of acetonitrile, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. Use of the composite solid polymer electrolyte according to any one of claims 1 to 5 in the preparation of a lithium-sulfur battery.

Images