Polymer-based solid electrolyte, preparation method thereof and solid-state lithium battery

Abstract

The invention relates to the technical field of batteries, and discloses a polymer-based solid electrolyte, a preparation method thereof and a solid-state lithium battery. The polymer-based solid electrolyte comprises a polymer, a lithium salt and an additive, wherein the additive comprises quaternary ammonium cations and fluorine ions. According to the invention, the additive of a specific type is doped in the polymer-based solid electrolyte, so that the ionic conductivity of the polymer-based solid electrolyte can be improved, and the problem of low ionic conductivity caused by high crystallinity of the polymer-based solid electrolyte is solved. And a LiF-rich interface protection layer can be constructed with Li < + > in the lithium salt in the charging and discharging process of the battery, so that the oxidation stability of the polymer-based solid electrolyte is improved, an electrochemical window is widened, the problem that the electrochemical window is narrow and cannot adapt to a high-voltage positive electrode is solved, meanwhile, the growth of lithium dendrites under high current density is inhibited, and the interface stability with a negative electrode is improved. Meanwhile, the polymer-based solid electrolyte has high mechanical strength, and the risk of being punctured by dendritic crystals is reduced.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a polymer-based solid electrolyte, its preparation method, and a solid-state lithium battery. Background Technology

[0002] With the increasing global demand for sustainable energy and the rapid development of the new energy industry, lithium-ion batteries, as one of the most widely used energy storage devices, occupy an important position in consumer electronics, electric vehicles, and large-scale energy storage. However, traditional liquid electrolytes have safety hazards such as flammability, leakage, and short circuits caused by lithium dendrite growth, and their energy density is gradually approaching its theoretical limit, making it difficult to meet the future demands for high-energy-density and high-safety energy storage. Against this backdrop, solid-state lithium batteries (such as solid-state lithium metal batteries) have become a research hotspot for next-generation energy storage technology due to the non-flammability of solid electrolytes, their ability to effectively suppress lithium dendrite growth, and their high theoretical specific capacity.

[0003] Solid-state electrolytes, as the core component of solid-state lithium metal batteries, can be mainly divided into three categories: inorganic solid-state electrolytes, polymer solid-state electrolytes, and organic-inorganic composite solid-state electrolytes. Inorganic solid-state electrolytes include oxide, sulfide, and halide solid-state electrolytes. Oxide solid-state electrolytes (such as garnet-type and NASICON-type) exhibit excellent chemical stability, particularly in suppressing lithium dendrite growth and demonstrating outstanding thermal stability, with a wide applicable temperature range. However, they generally suffer from high brittleness, high interfacial impedance with electrodes, and difficulty in processing. Sulfide solid-state electrolytes (such as glassy, ​​glass-ceramic, and Thio-LISICON) have high ionic conductivity, reaching up to 10⁻⁶ at room temperature. -3 S·cm -1 Some halogenated electrolytes can approach liquid electrolyte levels and exhibit good mechanical flexibility, allowing them to adapt to changes in electrode volume. However, they suffer from poor chemical stability and readily react with lithium metal or water and oxygen in the air. Halogenated solid electrolytes (such as Li3MX6 type and spinel type, where M is a metal and X is a halogen) have attracted attention in recent years due to their high ionic conductivity, and some types also possess good flexibility. However, the synthesis of some halide materials is challenging, and their long-term stability still requires optimization.

[0004] Organic-inorganic composite solid electrolytes combine inorganic fillers (such as oxide and sulfide particles) with a polymer matrix, giving them the flexibility of polymers and the high ionic conductivity and mechanical strength of inorganic materials. This improves interfacial compatibility, enhances ion transport efficiency, and increases resistance to lithium dendrite formation. However, some systems suffer from inorganic filler agglomeration and insufficient interfacial synergy, requiring further optimization of component dispersion and interfacial stability.

[0005] Polymer solid electrolytes have become a mainstream research direction due to their advantages such as good flexibility, good interfacial compatibility with electrode materials, and ease of processing and molding. However, polymer solid electrolytes also have some obvious drawbacks. Taking polyethylene oxide (PEO)-based polymer solid electrolytes as an example, the inherent high crystallinity of PEO severely restricts lithium-ion migration. The transport of lithium ions in PEO mainly depends on the movement of chain segments in amorphous regions. This structural characteristic results in a low ionic conductivity at room temperature, generally only reaching 10. -6 ~10 -5 S·cm -1 The high temperature (above 60°C) is required to reduce crystallinity and activate chain segment movement, which limits the charge and discharge performance of the battery at room temperature. Moreover, the mechanical strength of polymer solid electrolytes is insufficient, making it difficult to effectively prevent lithium dendrites from piercing and causing safety hazards. The electrochemical window is narrow, usually less than 4.0V, which cannot be adapted to high-voltage cathode materials, thus limiting the improvement of the overall energy density of the battery. These problems seriously restrict the progress of its commercial application.

[0006] Taking PEO-based solid electrolytes as an example, existing technologies mainly attempt to optimize the overall performance of polymer solid electrolytes through the following modification methods:

[0007] 1. Blending or copolymerization modification: By blending or copolymerizing with other polymers (such as polyethylene, polycarbonate, etc.), the skeletal effect of amorphous or block polymers is used to suppress PEO crystallization, thereby improving room temperature ionic conductivity and mechanical strength. Although this type of modification can improve some properties, it may lead to an increase in interfacial impedance due to increased polymer chain rigidity or poor compatibility, resulting in a decrease in ionic conductivity, or sacrifice of electrochemical stability (e.g., increased ionic conductivity but narrowed electrochemical window), failing to achieve a synergistic improvement in ionic conductivity, mechanical strength, and interfacial stability.

[0008] 2. Modification with plasticizers: Adding small molecule plasticizers (such as succinic anhydride, carbonate solvents, etc.) can improve ionic conductivity by reducing the crystallinity of PEO and increasing the flexibility of polymer segments and lithium-ion transport channels. However, this type of modification is often accompanied by problems such as decreased mechanical strength, high-temperature structural instability, or poor compatibility with the electrode interface.

[0009] 3. Inorganic filler filling: This method involves dispersing inorganic nanomaterials (such as alumina, lithium oxide, or metal-organic frameworks) in a PEO matrix to enhance mechanical properties and regulate ion transport pathways. However, inorganic fillers are prone to aggregation, leading to increased interfacial impedance and decreased ion transport efficiency, and may also trigger interfacial side reactions, affecting electrochemical stability.

[0010] 4. Interface Modification and Composite Structure Design: Multilayer composite films, cellulose support substrates, or other interface modification methods can be used to improve the mechanical strength and interfacial compatibility of PEO. However, these methods typically require complex processes and still struggle to simultaneously achieve high ionic conductivity and high-voltage electrode compatibility.

[0011] 5. Cross-linking network construction: A three-dimensional network structure is formed through chemical or physical cross-linking to inhibit PEO crystallization and improve mechanical strength.

[0012] The above modification methods mostly focus on optimizing a single performance and generally suffer from a "weakest link effect." For example, while improving ionic conductivity, they sacrifice mechanical strength or electrochemical window; or improving mechanical properties leads to decreased interfacial stability; or they are difficult to be compatible with high-voltage cathode materials. Currently, there is no mature technical solution that can comprehensively and effectively solve the problems faced by PEO-based solid electrolytes, and they cannot meet the requirements of high energy density and long cycle life of solid-state batteries.

[0013] Therefore, developing a novel modification strategy that can synergistically improve the ionic conductivity, mechanical strength, and high-voltage electrochemical stability of polymer solid electrolytes is a technical problem that urgently needs to be solved. Summary of the Invention

[0014] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a polymer-based solid electrolyte, a method for preparing the same, and a solid lithium battery.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] In a first aspect, the present invention provides a polymer-based solid electrolyte comprising a polymer, a lithium salt, and additives, wherein the additives comprise quaternary ammonium cations and fluoride ions.

[0017] The principle behind the conductivity of polymer-based solid electrolytes is as follows: Taking PEO-based solid electrolytes as an example, their conductivity depends on the interaction between the ether oxygen bonds on the PEO molecular chain and lithium ions (Li) in the lithium salt. + The "coordination-dissociation" cycle occurs between the ethylene oxide (EO) units in the PEO molecular chain. These ether oxygen atoms can react with lithium ions (Li₂O₃) released from the lithium salt. + It forms a stable solvation structure, similar to the solvation process of lithium ions in liquid electrolytes. However, since the transport of lithium ions in PEO mainly depends on the movement of amorphous region chain segments and relies on the solid polymer matrix to achieve ion transport, there are problems such as low lithium ion transport efficiency and low ionic conductivity.

[0018] This invention improves the ionic conductivity of polymer-based solid electrolytes by doping them with specific additives. Firstly, the quaternary ammonium cations in the additives disrupt the ordered arrangement of the polymer (e.g., PEO) molecular chains, reducing the electrolyte's crystallinity and increasing the proportion of amorphous regions. This provides more transport pathways for lithium ions, thereby enhancing the ionic conductivity of the polymer-based solid electrolyte and addressing the problem of low ionic conductivity caused by high crystallinity. Secondly, the fluoride ions in the additives can react with Li in the lithium salt during battery charging and discharging. + In-situ construction of a LiF-rich interface protective layer resulted in LiF exhibiting high mechanical strength, excellent electronic insulation, and good compatibility with Li. + The polymer-based solid electrolyte exhibits high conductivity and can tightly coat the electrode surface to form a stable SEI layer. Its main functions include: ① preventing continuous side reactions between the electrolyte and the electrode, enhancing the interfacial stability between the electrode and electrolyte, thereby suppressing performance degradation caused by interfacial deterioration during battery cycling, improving the compatibility of the electrolyte and electrode materials interface, and reducing interfacial impedance; ② physically blocking the growth and penetration of lithium dendrites, ultimately improving the cycle stability and safety of the battery; ③ enhancing the oxidation stability of the polymer-based solid electrolyte, broadening the electrochemical window to accommodate high-voltage cathode materials above 4.2V, solving the problem of its narrow electrochemical window preventing compatibility with high-voltage cathodes, while simultaneously suppressing lithium dendrite growth at high current densities and improving interfacial stability with the anode (e.g., lithium metal anode). In summary, the polymer-based solid electrolyte of this invention can effectively improve the electrochemical performance of batteries.

[0019] Preferably, the quaternary ammonium cation includes at least one selected from tetraethylammonium, tetrabutylammonium, alkyltriethylammonium, and alkyltributylammonium.

[0020] Preferably, the additive is tetrabutylammonium fluoride (chemical formula C). 16 H 36 FN, TBAF).

[0021] Preferably, the additive has a mass content of 2% to 15% in the polymer-based solid electrolyte, for example, it can be 2%, 3%, 4%, 5%, 6%, 8%, 10%, 11%, 12%, 13%, 14%, or 15%, and is more preferably 5% to 10%. Within the above-mentioned preferred content range, high ionic conductivity, good mechanical strength, and interfacial stability can be better balanced, which is beneficial to improving the overall electrochemical performance of the battery.

[0022] Preferably, the polymer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinylidene chloride, and polypropylene oxide, and is preferably polyethylene oxide.

[0023] Preferably, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalateborate) and lithium arsenate, and is preferably lithium bis(trifluoromethanesulfonyl)imide.

[0024] Preferably, the molar ratio of the lithium salt to the polymer is (1~3):(9~7), wherein the lithium salt is selected from the range of "1~3", for example, it can be 1, 1.5, 2, 2.5 or 3, etc.; the polymer is selected from the range of "9~7", for example, 9, 8.5, 8, 7.5 or 7, etc.

[0025] In a second aspect, the present invention provides a method for preparing a polymer-based solid electrolyte as described in the first aspect, the method comprising the following steps:

[0026] The polymer, lithium salt, and additives are dissolved in an organic solvent to reduce the crystallinity of the polymer, and then dried to obtain a polymer-based solid electrolyte.

[0027] The method of the present invention dissolves polymers, lithium salts and additives in an organic solvent, thereby making the components uniformly mixed. The additives can reduce the crystallinity of the polymer, increase the ionic conductivity of the solid electrolyte, and improve mechanical properties and high voltage stability.

[0028] The preparation method of polymer-based solid electrolyte provided by this invention has the advantages of simple preparation process, easy large-scale continuous production, easy commercialization, and broad application prospects.

[0029] Preferably, the organic solvent includes at least one of acetone, acetonitrile, N-methylpyrrolidone (NMP), and polypropylene carbonate (PPC), with acetonitrile being the most preferred. However, it is not limited to the types listed above, and other organic solvents commonly used in the art that can dissolve polymers, lithium salts, and additives are also suitable for this invention.

[0030] Preferably, the polymer, lithium salt, and additives are dissolved in an organic solvent and then stirred.

[0031] Preferably, the stirring temperature is 20℃~60℃, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, etc.

[0032] Preferably, the stirring time is 48h to 75h, for example, it can be 48h, 50h, 52h, 55h, 58h, 60h, 62h, 65h, 68h, 70h, 73h or 75h.

[0033] In one embodiment, the stirring method is magnetic stirring.

[0034] Preferably, the drying is carried out in a mold to obtain a polymer-based solid electrolyte membrane.

[0035] In one embodiment, a polymer-based solid electrolyte membrane can be prepared by casting a mixture of polymer, lithium salt, additives and organic solvent into a mold.

[0036] Preferably, the thickness of the polymer-based solid electrolyte membrane is 100μm to 150μm, for example, it can be 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm, 145μm or 150μm, etc.

[0037] Thirdly, the present invention provides a solid-state lithium battery, wherein the lithium battery includes the polymer-based solid electrolyte described in the first aspect, or the polymer-based solid electrolyte prepared by the method described in the second aspect.

[0038] The solid-state lithium battery of the present invention can be adapted to high-voltage cathode materials, which can improve the energy density of the battery, and it has good long cycle life and good safety performance.

[0039] In one embodiment, the solid-state lithium battery includes a positive electrode, a negative electrode, and a solid electrolyte, wherein the solid electrolyte is the polymer-based solid electrolyte described in the first aspect, or the polymer-based solid electrolyte prepared by the method described in the second aspect.

[0040] In one embodiment, the negative electrode is a lithium metal negative electrode. Compared to other negative electrodes, the lithium metal negative electrode has a higher theoretical specific capacity, which can significantly improve the energy density of the battery. Meanwhile, the introduction of the polymer-based solid electrolyte of this invention can suppress dendrite growth, and its high mechanical strength reduces the risk of dendrite puncture.

[0041] In one embodiment, the lithium metal anode may be at least one of lithium foil, lithium sheet, or lithium alloy.

[0042] In another embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector, the negative electrode active layer including a negative electrode active material, the negative electrode active material including at least one of titanium-based negative electrode material or hard carbon.

[0043] In one embodiment, the positive current collector includes at least one of aluminum foil, carbon-coated aluminum foil, or stainless steel foil.

[0044] In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, which includes at least one of lithium iron phosphate, lithium vanadium phosphate, lithium manganese oxide, lithium titanium chloride, or lithium cobalt oxide.

[0045] In one embodiment, the positive electrode active layer further includes a binder and a conductive agent, wherein the binder includes at least one of polyvinylidene fluoride, polyamide, polyvinyl alcohol or carboxymethyl cellulose, and the conductive agent includes at least one of acetylene black, Ketjen black or Super P.

[0046] Compared with existing technologies, the present invention has the following beneficial effects:

[0047] This invention improves the ionic conductivity of polymer-based solid electrolytes by doping them with specific additives, thus addressing the problem of low ionic conductivity caused by high crystallinity. Furthermore, it allows the electrolyte to react with Li in lithium salts during battery charging and discharging. + By constructing a LiF-rich interfacial protective layer, the oxidation stability of the polymer-based solid electrolyte is improved, and the electrochemical window is broadened, solving the problem that its narrow electrochemical window cannot be adapted to high-voltage cathodes. Simultaneously, it suppresses lithium dendrite growth under high current density, improving interfacial stability with the anode. Furthermore, the polymer-based solid electrolyte of this invention exhibits high mechanical strength, reducing the risk of dendrite puncture. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the preparation process of a polymer-based solid electrolyte in one embodiment of the present invention.

[0049] Figure 2 These are XRD comparison spectra of the polymer-based solid electrolytes of Example 3 and Comparative Example 1, where PEO-LiTFSI corresponds to Comparative Example 1 and PEO-LiTFSI-8%TBAF corresponds to Example 3. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0051] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0052] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0053] Example 1

[0054] This embodiment provides a polymer-based solid electrolyte, which includes a polymer (polyethylene oxide, PEO), a lithium salt (lithium bis(trifluoromethanesulfonylimide, LiTFSI)) and an additive (tetrabutylammonium fluoride, TBAF). The additive has a mass content of 2% in the polymer-based solid electrolyte, and the molar ratio of lithium salt to polymer is 1:9.

[0055] This embodiment also provides a method for preparing the above-mentioned polymer-based solid electrolyte; see the schematic diagram of the preparation process. Figure 1 This includes the following steps:

[0056] First, PEO and LiTFSI were dried separately in a desiccator for 24 hours to remove moisture. Then, the following preparation process was carried out in a glove box: 1.0000 g of PEO (Mv = 600000) and a certain amount of LiTFSI (purity 99.5%, molar ratio of Li to ethylene oxide EO 1:9) were weighed out. PEO and LiTFSI were dissolved in 20 mL of acetonitrile (purity 99.8%) and stirred at 30 °C with a magnetic stirrer for 24 hours until a homogeneous, transparent, viscous solution was formed. Subsequently, 2% (by mass) of TBAF (based on the total mass of PEO and LiTFSI) was added to the above viscous solution, and the mixture was stirred thoroughly for 48 hours to ensure that TBAF was uniformly mixed with the solution. Afterward, the well-mixed solution was allowed to stand for 2 hours until all air bubbles disappeared. Then, the solution was poured into a clean, circular polytetrafluoroethylene (PTFE) mold with a diameter of 19 mm and a depth of 1 mm. The mold was then dried in a glove box for 24 hours. Once the solution was completely dry, it was peeled off along the edge of the PTFE plate using tweezers to obtain the polymer-based solid electrolyte membrane, abbreviated as PEO-LiTFSI-2%TBAF solid electrolyte. The membrane thickness was measured to be 120 μm using calipers and stored in an argon-filled glove box (H2O content <0.01 ppm, O2 content <0.01 ppm) to prevent water and oxygen contamination.

[0057] This embodiment also provides a solid-state lithium battery, the preparation method of which includes:

[0058] (1) Preparation of positive electrode sheet

[0059] First, the positive electrode active material lithium iron phosphate (LiFePO4, LFP), conductive agent (Super P), and binder (PVDF) were weighed in a mass ratio of 8:1:1, and thoroughly mixed and ground until homogeneous. Next, an appropriate amount of NMP solvent was added, and grinding continued until the slurry reached the desired viscosity. Then, the slurry was evenly coated onto the surface of carbon-coated aluminum foil using a doctor blade and pre-dried in a 60°C forced-air drying oven. Afterward, it was transferred to a vacuum drying oven and dried at 120°C for 12 hours. After the sample cooled naturally, the electrode sheet was cut into 11mm diameter round pieces using a cutting machine and stored in a glove box for later use.

[0060] (2) Assembly of all-solid-state lithium metal batteries

[0061] In an argon-filled glove box (where oxygen and moisture content are both below 0.01 ppm), an all-solid-state lithium metal battery was assembled using the polymer-based solid electrolyte membrane and positive electrode prepared in this embodiment, following the standard 2032 coin cell assembly process. The assembly sequence was: negative electrode shell, spring sheet, gasket, lithium sheet, polymer-based solid electrolyte membrane, positive electrode, and positive electrode shell. After assembly, the entire battery was placed in a coin cell packaging machine and sealed under a pressure of 50 MPa. To increase the contact between the electrode and the electrolyte membrane and reduce the interface resistance, the battery was then left to stand in a 60°C constant temperature chamber for 6 hours.

[0062] (3) Assembly of stainless steel symmetrical batteries

[0063] Stainless steel (SS) sheets were selected as the reference electrode, and stainless steel symmetric cells were assembled in an argon-filled glove box (where oxygen and moisture content were both below 0.01 ppm). The assembly sequence was: negative electrode shell, spring sheet, stainless steel gasket, polymer-based solid electrolyte membrane, stainless steel gasket, and positive electrode shell. After assembly, the stainless steel symmetric cells were placed in a coin cell packaging machine and sealed under a pressure of 50 MPa. The assembled cells were then placed in a 30°C oven and left to stand for 1 hour.

[0064] (4) Assembly of Li||SPEs||SS button half-cells

[0065] In an argon-filled glove box (where oxygen and moisture content are both below 0.01 ppm), a lithium metal sheet was used as the reference electrode, a 304 stainless steel sheet as the working electrode, and a Li||SPEs||SS coin cell was assembled using the polymer-based solid electrolyte membrane prepared in this embodiment. The assembly sequence was: negative electrode shell, spring sheet, 304 stainless steel gasket, polymer-based solid electrolyte membrane, lithium metal sheet, and positive electrode shell. After assembly, the battery was placed in a coin cell packaging machine and sealed under a pressure of 50 MPa. The assembled battery was then placed in a 60°C oven for 2 hours.

[0066] Example 2

[0067] The difference between this embodiment and Embodiment 1 is that the additive in the polymer-based solid electrolyte has a mass content of 5%.

[0068] Example 3

[0069] The difference between this embodiment and Embodiment 1 is that the mass content of the additive in the polymer-based solid electrolyte is 8%.

[0070] Example 4

[0071] The difference between this embodiment and Embodiment 1 is that the additive in the polymer-based solid electrolyte has a mass content of 10%.

[0072] Example 5

[0073] The difference between this embodiment and Embodiment 1 is that the additive has a mass content of 12.5% ​​in the polymer-based solid electrolyte.

[0074] Example 6

[0075] The difference between this embodiment and Embodiment 1 is that the additive in the polymer-based solid electrolyte has a mass content of 15%.

[0076] Example 7

[0077] The difference between this embodiment and Embodiment 1 is that the additive has a mass content of 6% in the polymer-based solid electrolyte, PEO is replaced with polyvinylidene fluoride (PVDF), LiTFSI is replaced with lithium bis(oxalate-borate), and the molar ratio of lithium bis(oxalate-borate) to PVDF is adjusted.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that the polymer-based solid electrolyte does not contain TBAF.

[0080] Performance tests were conducted on the batteries in Examples 1-7 and Comparative Example 1:

[0081] (1) Cyclic performance test of all-solid-state lithium metal battery: Cyclic performance test was conducted using a Blue Electric charge-discharge tester at an operating temperature of 60℃. The test voltage range was 2.5-3.8V, and the charge-discharge rate was 0.5C (where 0.1C corresponds to 170mAh·g). -1 After 100 cycles of testing, the capacity retention rate was calculated based on the initial discharge capacity and the discharge specific capacity after 100 cycles. The capacity retention rate = discharge specific capacity after 100 cycles / initial discharge specific capacity × 100%. The results are shown in Table 1.

[0082]

[0083] As shown in Table 1, the present invention improves the cycle performance of the battery by introducing TBAF into the polymer-based solid electrolyte and applying it to the battery. In contrast, the polymer-based solid electrolyte of D1 does not contain TBAF, and its cycle capacity retention rate is only 75.0%. Moreover, the discharge specific capacity of the battery shows a trend of first increasing and then decreasing, and the discharge capacity is higher when the content of the additive TBAF is 5wt%~8wt%.

[0084] Meanwhile, as can be seen from Examples 1-6, there is an optimal range for the amount of TBAF added. Within the range of 5% to 10%, the effect of improving cycle performance is better.

[0085] (2) Electrochemical Impedance Spectroscopy (EIS) Test of Stainless Steel Symmetric Cells: Using a Princeton electrochemical workstation, EIS tests were performed in the frequency range of 0.01 Hz-1 MHz with an amplitude of 10 mV. The obtained impedance values ​​were used to calculate the ionic conductivity. The test temperatures were 30℃, 40℃, 50℃, 60℃, 70℃, and 80℃. Before recording the impedance response, the cell was kept at the corresponding temperature for at least 1 h. The thickness of the electrolyte was measured with vernier calipers (120 μm in Example 1). The bulk impedance of the electrolyte was fitted. Combined with the effective contact area between the polymer-based solid electrolyte membrane and the stainless steel gasket (the diameter of the stainless steel gasket was 15.8 mm), the ionic conductivity σ of the polymer-based solid electrolyte (unit: S·cm) was calculated using Formula 1. -1 Formula 1 is:

[0086] ;

[0087] Where σ represents ionic conductivity (unit: S·cm) -1 L represents the thickness of the polymer-based solid electrolyte membrane (in cm), R represents the bulk impedance of the polymer-based solid electrolyte membrane (in Ω), and A represents the electrode area (in cm²). 2 ).

[0088] The results are shown in Table 2.

[0089]

[0090] Table 2 shows that the present invention, by introducing TBAF into the polymer-based solid electrolyte, can improve the ionic conductivity of the polymer-based solid electrolyte at different temperatures. Furthermore, the ionic conductivity is higher when the TBAF content is 8wt%~10wt%, indicating that at this content, TBAF has the most significant effect on optimizing the ion transport path and increasing the free ion concentration. When the TBAF content is greater than 10%, the ionic conductivity decreases, because excessive TBAF content hinders ion migration and reduces ionic conductivity.

[0091] Meanwhile, as the temperature increases, the ionic conductivity of all polymer solid electrolytes shows an upward trend. This is because the increased temperature enhances the mobility of polymer chain segments, thereby improving the ionic conductivity.

[0092] (3) Linear scan voltammetry (LSV) was performed on Li||SPEs||SS coin half-cells: the test temperature was 60℃, and a Princeton electrochemical workstation was used with an LSV of 10mV·s. -1 The scan rate is in the range of 3~6V (relative to Li). + The Li||SPEs||SS system was tested by linear sweep voltammetry (LSV) within the potential range of / Li, and the results are shown in Table 3.

[0093]

[0094] As shown in Table 3, the electrolyte in Comparative Example 1 began to decompose at 4.53V, while the decomposition voltages of the solid electrolytes in Examples 1-7 were all higher than those in Comparative Example 1. This indicates that the present invention improves the oxidative stability of the polymer-based solid electrolyte and enhances its antioxidant capacity. This is due to the F in TBAF. - It participates in the formation of a LiF-rich interface layer, inhibiting the oxidative decomposition of the electrolyte. The solid electrolyte's excellent oxidation resistance allows it to be matched with higher-voltage cathode materials, which is beneficial for improving the battery's energy density.

[0095] Meanwhile, as can be seen from Examples 1-6, there is an optimal range for the amount of TBAF added. Within the range of 5% to 10%, the effect of improving cycle performance is better.

[0096] XRD tests were performed on the polymer-based solid electrolytes of Example 3 and Comparative Example 1. XRD comparison spectra are shown below. Figure 2 In Example 1, PEO-LiTFSI corresponds to Example 1, and PEO-LiTFSI-8%TBAF corresponds to Example 3. As shown in the figure, PEO-LiTFSI has sharp diffraction peaks near 19° and 23°, corresponding to the (120) and (112) crystal planes of its orthorhombic crystal system, indicating that pure PEO has high crystallinity and its PEO chain segments are highly ordered. After adding 8% TBAF, PEO-LiTFSI-8%TBAF is formed, and the intensity of the diffraction peaks near 19° and 23° is significantly reduced, indicating that the addition of TBAF effectively inhibits the crystallization behavior of PEO and increases the amorphous region and disorder of the molecular chains in CSE. Furthermore, after adding TBAF, no new diffraction peaks appear in the XRD pattern, indicating that TBAF is uniformly dispersed in the PEO-LiTFSI matrix and does not form an independent crystalline phase.

[0097] Using the polymer-based solid electrolytes of Example 3 and Comparative Example 1, lithium-ion symmetric batteries (Li||SPEs||Li) were assembled in an argon-filled glove box (where oxygen and moisture content were both below 0.01 ppm). The assembly sequence was: negative electrode shell, spring sheet, gasket, lithium metal sheet, polymer-based solid electrolyte, lithium metal sheet, and positive electrode shell. After assembly, the battery was placed in a coin cell packaging machine and sealed under a pressure of 50 MPa. To increase the contact between the electrode and the electrolyte membrane and reduce the interfacial resistance, the battery was then placed in a constant temperature chamber at 60°C for 6 hours.

[0098] Rate performance testing was performed on the aforementioned lithium symmetric battery: constant current cycling tests were conducted on the battery at different current densities using a Blue Electric charge-discharge tester. The current density was set to 0.05 mA·cm². -2 ~0.5mA·cm -2 The cyclic deposition / stripping time was set to 0.5 h, and the critical current density was recorded. The results are shown in Table 4.

[0099] Table 4

[0100] sample Solid electrolyte composition and ratio (molar ratio) Add TBAF content (wt%) <![CDATA[Critical current density (mA·cm -2 ).]]> Example 3 LiTFSI:PEO (1:9) 8% 0.65 Comparative Example 1 LiTFSI:PEO (1:9) none 0.45

[0101] As shown in Table 4, the critical current density of the polymer-based solid electrolyte in Example 3 is 0.65 mA·cm⁻¹. -2 This indicates that when the current density increases to 0.65 mA·cm -2 At this point, lithium dendrites pierce the electrolyte, causing an internal short circuit in the battery, while the critical current density of the solid electrolyte in Comparative Example 1 is only 0.45 mA·cm⁻¹. -2 This demonstrates that the present invention reduces the risk of lithium dendrite puncture by introducing TBAF into the polymer-based solid electrolyte, which is due to the significant improvement in the mechanical properties of the polymer-based solid electrolyte.

[0102] In summary, this invention, by doping specific types of additives into polymer-based solid electrolytes, not only improves the ionic conductivity of the polymer-based solid electrolyte, solving the problem of low ionic conductivity caused by its high crystallinity, but also allows it to react with Li in lithium salts during battery charging and discharging. + By constructing a LiF-rich interfacial protective layer, the oxidation stability of the polymer-based solid electrolyte is improved, and the electrochemical window is broadened, solving the problem that its narrow electrochemical window cannot be adapted to high-voltage cathodes. Simultaneously, it suppresses lithium dendrite growth under high current density, improving interfacial stability with the anode. Furthermore, the polymer-based solid electrolyte of this invention exhibits high mechanical strength, reducing the risk of dendrite puncture.

[0103] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A polymer-based solid-state electrolyte, characterized by, The polymer-based solid electrolyte comprises a polymer, a lithium salt and an additive, wherein the additive comprises a quaternary ammonium cation and a fluoride ion.

2. The polymer-based solid-state electrolyte of claim 1, wherein, The quaternary ammonium cation comprises at least one of tetraethylammonium, tetrabutylammonium, alkyltriethylammonium and alkyltributylammonium. Preferably, the additive is tetrabutylammonium fluoride.

3. The polymer-based solid-state electrolyte according to claim 1 or 2, characterized in that, The additive has a mass content of 2% to 15% in the polymer-based solid electrolyte, preferably 5% to 10%.

4. The polymer-based solid-state electrolyte according to any one of claims 1 to 3, characterized in that, The polymer comprises at least one of polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinylidene chloride and polypropylene oxide, preferably polyethylene oxide.

5. The polymer-based solid-state electrolyte according to any one of claims 1 to 4, characterized in that, The lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate and lithium arsenic fluoride, preferably lithium bis(trifluoromethanesulfonyl)imide.

6. The polymer-based solid-state electrolyte according to any one of claims 1 to 5, wherein The molar ratio of the lithium salt to the polymer is (1-3):(9-7).

7. A method of producing a polymer-based solid-state electrolyte as claimed in any one of claims 1 to 6, characterized in that, The preparation method comprises the following steps: dissolving the polymer, the lithium salt and the additive in an organic solvent to reduce the crystallinity of the polymer, and drying to obtain the polymer-based solid electrolyte.

8. The method for preparing the polymer-based solid electrolyte according to claim 7, characterized in that, The organic solvent comprises at least one of acetone, acetonitrile, N-methylpyrrolidone and polypropylene carbonate, preferably acetonitrile.

9. The method for producing a polymer-based solid electrolyte according to claim 7 or 8, characterized by, After dissolving the polymer, the lithium salt and the additive in the organic solvent, stirring is performed; Preferably, the temperature of the stirring is 20°C to 60°C; Preferably, the time of the stirring is 48h to 75h; Preferably, the drying is performed in a mold to obtain a polymer-based solid electrolyte film; Preferably, the thickness of the polymer-based solid electrolyte film is 100μm to 150μm.

10. A solid-state lithium battery, characterized by, The solid-state lithium battery comprises the polymer-based solid electrolyte according to any one of claims 1-6, or the polymer-based solid electrolyte prepared by the method according to claim 7 or 8.

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