In-situ polymerization gel electrolyte, preparation method and application thereof

Abstract

The invention relates to the technical field of new energy, in particular to an in-situ polymerization gel electrolyte, a preparation method and application of the in-situ polymerization gel electrolyte, the in-situ polymerization gel electrolyte comprises conducting salt, an additive and a boron-containing polymer monomer, and preparation of the gel electrolyte is completed by initiating a cross-linking polymerization reaction of a precursor solution through heating. The in-situ polymerization gel electrolyte is applied to a quasi-solid alkali metal secondary battery. The gel electrolyte disclosed by the invention has relatively high ionic conductivity and relatively good lithium ion transference number, and can be used for preparing a quasi-solid negative-electrode-free lithium metal battery with high cycle and high safety performance. Meanwhile, the process flow for preparing the quasi-solid negative-electrode-free lithium metal battery by adopting the in-situ polymerization gel electrolyte is simple, and large-scale industrial production is easy to realize.

Description

Technical Field

[0001] This invention relates to an in-situ polymerized gel electrolyte, its preparation method, and its application, belonging to the field of new energy technology. Background Technology

[0002] Energy is a vital material foundation for developing the national economy and improving people's living standards, and it is also a crucial factor directly influencing economic development. Since the beginning of the 21st century, the problems of resource shortages, environmental pollution, and the greenhouse effect caused by traditional energy utilization methods have become increasingly prominent. Improving the energy structure and developing efficient and clean new energy sources has become a global consensus. Lithium / sodium-ion batteries have gained popularity due to their superior performance, including safety, environmental friendliness, high specific energy, and excellent electrochemical performance. Currently used lithium / sodium-ion batteries employ liquid electrolytes (LE), which have drawbacks such as electrolyte leakage and flammability during use. To ensure the safety and stability of batteries during use, the development direction of lithium / sodium-ion batteries is gradually shifting towards solid-state batteries.

[0003] Solid-state polymer electrolytes have garnered widespread attention due to their superior safety. They are stable and can be matched with high-voltage cathodes and lithium metal anodes, further improving battery energy density. Secondly, polymer electrolytes are lightweight, resulting in smaller overall mass and volume for the same energy density in lithium-ion batteries. Furthermore, polymer electrolytes possess excellent mechanical properties, leading to better interfacial contact with both the positive and negative electrodes.

[0004] While polymer electrolytes offer significant advantages, they also suffer from drawbacks such as low ionic conductivity at room temperature and a narrow electrochemical window. Current research on polymer electrolytes primarily focuses on polyethylene glycol (PEG) polyether lithium salt systems or polyether electrolyte systems prepared by the ring-opening polymerization of 1,3-dioxolane (DOL). For example, Chinese patent application CN101183727A discloses a modified inorganic nanoparticle-reinforced PEO / lithium salt all-solid-state polymer electrolyte; Chinese patent application CN102709597A presents a composite all-solid-state electrolyte comprising a dimethylsiloxane-ethylene oxide copolymer, a lithium salt, and nano-inorganic fillers.

[0005] Research on in-situ polymerized polyether electrolytes mainly focuses on the preparation of polyether electrolytes using the ring-opening polymerization of 1,3-dioxolane (DOL), as exemplified by Chinese patent application CN116190776A. However, the poor high-voltage resistance of the repeating chain units of poly(1,3-dioxolane) (P-DOL) and the low lithium-ion transference number in this system severely hinder the application of in-situ polymer solid electrolytes in lithium batteries.

[0006] Therefore, there is an urgent need to develop novel polyether polymer electrolytes to achieve in-situ polymerization and solve the problems of high solid / solid interface impedance between battery electrodes / solid electrolytes, as well as the poor mechanical properties, low conductivity and migration number of ordinary gel electrolytes, and the difficulty in effectively suppressing lithium dendrite growth, which leads to poor lithium metal and battery cycle stability. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing an in-situ polymerized gel electrolyte, its preparation method, and its application. It solves the problems of high solid / solid interface impedance between battery electrodes and solid electrolytes, as well as the poor mechanical properties, low conductivity and migration number of ordinary gel electrolytes, and the difficulty in effectively suppressing lithium dendrite growth, which leads to poor lithium metal and battery cycle stability.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: an in-situ polymerized gel electrolyte, wherein the in-situ polymerized gel electrolyte contains a boron-containing polymer monomer, and the structural formula of the boron-containing polymer monomer is shown in Formula I below:

[0009]

[0010] In Equation I, R1, R2, and R3 can be independently chosen from any of the following structural formulas:

[0011] * indicates a connection site.

[0012] Furthermore, the boron-containing polymer monomer is selected from at least one of the following structural formulas:

[0013]

[0014] Furthermore, the in-situ polymerized gel electrolyte comprises a conductive salt, an additive, and the boron-containing polymer monomer, wherein the additive is a fluorinated piperine compound.

[0015] Furthermore, by weight, the in-situ polymerized gel electrolyte comprises: 13-30 parts of the conductive salt, 1-10 parts of the additive, and 55-85 parts of the boron-containing polymer monomer.

[0016] Furthermore, the conductive salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, and lithium bis(fluorosulfonyl)imide.

[0017] Furthermore, the additive is a compound of formula II as follows:

[0018]

[0019] The present invention also discloses a method for preparing an in-situ polymerized gel electrolyte. The method comprises: mixing a conductive salt, an additive, and the boron-containing polymer monomer evenly to obtain an in-situ polymerized gel electrolyte precursor solution; and initiating a cross-linking in-situ polymerization reaction in the precursor solution in a battery by heating to obtain the in-situ polymerized gel electrolyte.

[0020] Furthermore, the crosslinking polymerization reaction temperature is 30–80°C.

[0021] The present invention also discloses an application of an in-situ polymerized gel electrolyte, which is used in quasi-solid-state alkali metal secondary batteries.

[0022] Furthermore, after the conductive salt, additives and the boron-containing polymer monomer are mixed evenly, an in-situ polymerized gel electrolyte precursor solution is obtained. The precursor solution is injected between the positive and negative electrodes of the assembled battery, and then in-situ ring-opening polymerization and solidification are achieved by heating to obtain an integrated quasi-solid-state alkali metal secondary battery.

[0023] The beneficial effects of this invention are:

[0024] (1) The present invention uses in-situ polymerization to prepare quasi-solid gel electrolyte alkali metal secondary batteries, so that the solid electrolyte formed can achieve full contact with the electrode, which solves the problems of poor interface contact, high impedance and poor cycle performance of conventional solid batteries.

[0025] (2) When the in-situ polymerized gel electrolyte is formed by combining boron-containing polymer monomers with high-boiling-point difluoropiperidine ring organic compounds, the conductivity at 25℃ can reach 5.3×10⁻⁶. -4 S·cm -1 ~9.7×10 -3 S·cm -1 Simultaneously, by utilizing the electron-deficient properties of boron atoms, the anions of electrolyte salts can be effectively complexed, thereby increasing the degree of dissociation of the electrolyte salts and enabling the lithium-ion transference number to reach 0.71–0.80.

[0026] (3) The preparation of the in-situ polymerized gel electrolyte can be initiated by heating in the presence of conductive salt, without the need to use azo compounds or peroxides as initiators, thus avoiding the problem of increased internal resistance caused by the high-temperature decomposition of azo compounds or peroxides and the generation of bubbles.

[0027] (4) The gel electrolyte described in this invention has high ionic conductivity and good lithium-ion transference number, and can be used to prepare quasi-solid-state electrodeless lithium metal batteries with high cycle life and high safety performance. At the same time, the process of preparing quasi-solid-state electrodeless lithium metal batteries using the in-situ polymerized gel electrolyte described in this invention is simple and easy to realize large-scale industrial production. Detailed Implementation

[0028] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0030] An in-situ polymerized gel electrolyte, wherein the in-situ polymerized gel electrolyte contains a boron-containing polymer monomer, the structural formula of which is shown in Formula I below:

[0031]

[0032] In Equation I, R1, R2, and R3 can be independently chosen from any of the following structural formulas:

[0033] * indicates a connection site.

[0034] Specifically, the boron-containing polymer monomer is selected from at least one of the following structural formulas:

[0035]

[0036] Specifically, the in-situ polymerized gel electrolyte includes a conductive salt, an additive, and the boron-containing polymer monomer, wherein the additive is a fluorinated piperine compound.

[0037] Specifically, by weight, the in-situ polymerized gel electrolyte comprises: 13-30 parts of the conductive salt, 1-10 parts of the additive, and 55-85 parts of the boron-containing polymer monomer.

[0038] Specifically, the conductive salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, and lithium bis(fluorosulfonyl)imide.

[0039] Specifically, the additive is a compound of formula II as follows:

[0040]

[0041] A method for preparing an in-situ polymerized gel electrolyte, the method comprising: mixing a conductive salt, an additive and a boron-containing polymer monomer uniformly to obtain an in-situ polymerized gel electrolyte precursor solution; wherein the precursor solution is subjected to a cross-linking in-situ polymerization reaction initiated by heating in a battery to obtain the in-situ polymerized gel electrolyte.

[0042] Specifically, the crosslinking polymerization reaction temperature is 30–80°C, and the crosslinking polymerization is initiated by heating for 1–24 hours.

[0043] An application of an in-situ polymerized gel electrolyte, wherein the in-situ polymerized gel electrolyte is used in a quasi-solid-state alkali metal secondary battery.

[0044] Specifically, after the conductive salt, additives and the boron-containing polymer monomer are mixed evenly, an in-situ polymerized gel electrolyte precursor solution is obtained. The precursor solution is injected between the positive and negative electrode plates of the assembled battery, and then in-situ ring-opening polymerization and solidification are achieved by heating to obtain an integrated quasi-solid-state alkali metal secondary battery.

[0045] Specifically, the quasi-solid-state alkali metal secondary battery includes a positive electrode, an in-situ polymerized gel electrolyte, a separator, and a negative electrode;

[0046] The positive electrode is a coated positive electrode containing a positive electrode active material, wherein the positive electrode active material is a lithium-containing positive electrode active material or a sodium-containing positive electrode active material.

[0047] Preferably, the positive electrode active material is lithium cobalt oxide, lithium manganese oxide, ternary nickel-cobalt-manganese lithium, nickel-manganese lithium oxide, lithium iron phosphate, lithium manganese iron phosphate, sodium vanadium phosphate, and layered oxide Na. 0.44 At least one of MnO2.

[0048] The negative electrode is an active metal foil, or a coated electrode containing a negative electrode active material. The negative electrode active material is preferably artificial graphite, natural graphite, lithium titanate, lithium metal, silicon-carbon composite material, hard carbon, sodium metal, or sodium alloy.

[0049] The diaphragm is at least one of a polyolefin membrane, a cellulose membrane, or a glass fiber membrane.

[0050] 1. Synthesis example

[0051] Synthesis example 1

[0052] (Taking BOX-4 as an example, the preparation method is referenced in Chemistry-A European Journal (2011), 17(9), 2689-2697, S2689 / 1-S2689 / 83)

[0053] Take 30.6g of (3-methylepoxybutane-3-yl)methanol, 13.7g of tetraacetyl diboronic anhydride and 200g of THF, heat them to 150-160℃ in a pressure-resistant bottle, keep the temperature for 6.0h, stop heating, and desolvent under reduced pressure until no fraction is distilled. Further reduce the pressure and distillation apparatus to obtain 3.1g of BOX-4.

[0054] 11B NMR (128MHz): solvent deuterated chloroform, δ (ppm): 12.31ppm, GC-MS: 314.

[0055] Synthesis example 2

[0056] (Taking BOX-2 as an example, the preparation method is referenced in Chemistry-A European Journal (2011), 17(9), 2689-2697, S2689 / 1-S2689 / 83)

[0057] Take 32.0 g of (1,3-dioxacyclopentan-4-yl)methanol, 13.7 g of tetraacetyl diboronic anhydride and 200 g of THF, heat them to 150-160 °C in a pressure-resistant flask, keep the temperature for 8.0 h, stop heating, and remove the solvent under reduced pressure until there are no fractions. Further reduce the pressure and distill to obtain 3.0 g of BOX-2.

[0058] 11B NMR (128MHz): solvent deuterated chloroform, δ (ppm): 14.31ppm, GC-MS: 320.

[0059] II. Examples of In-situ Polymerized Gel Electrolyte and Battery Preparation

[0060] Example 1

[0061] In an argon-filled glove box, LiTFSI and LiPF6 are added to the additive shown in Formula II and the boron-containing in-situ polymerization monomer BOX-1, and the mixture is magnetically stirred for 10 minutes to obtain a clear in-situ polymerization gel electrolyte precursor solution; wherein the mass ratio of the boron-containing in-situ polymerization monomer BOX-1, the additive shown in Formula II, LiPF6, and LiTFSI is 63:10:2:25.

[0062] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and the SL / / SL battery was subjected to polymerization at 80°C for 1 hour. The ionic conductivity of the in-situ polymerized gel electrolyte was then tested. A lithium-lithium symmetric battery was assembled, and the lithium-ion transference number was tested.

[0063] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room-temperature ionic conductivity of 9.7 × 10⁻⁶. -3 S / cm, lithium-ion transference number 0.80.

[0064] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2 The areal density of the coating is applied (on aluminum foil), and the coating is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, and vacuum baked at 100°C for 48 hours. The in-situ polymerized gel electrolyte precursor solution described in this embodiment is then injected, and in-situ polymerization is carried out at 30°C. The mixture is then sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0065] A full-cell test was conducted on the quasi-solid-state electrodeless lithium metal battery, and the first-cycle discharge specific capacity was 155.3 mAh g. -1 The initial coulombic efficiency was 93.19%; the coulombic efficiency was close to 100% during the cycle; and the capacity retention rate was still 68.37% after 300 cycles. After the first charge of the battery, the lithium deposition morphology on the current collector surface was dense, and no lithium dendrites were generated.

[0066] Example 2

[0067] In an argon-filled glove box, LiPF6 is added to the additive shown in Formula II and the liquid in-situ polymerization monomer BOX-2, and the mixture is magnetically stirred for 10 minutes to obtain a clear in-situ polymerization gel electrolyte precursor solution; wherein the mass ratio of boron-containing in-situ polymerization monomer BOX-2, additive shown in Formula II, and LiPF6 is 82:1:17.

[0068] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and polymerized in the SL / / SL cell at 30°C for 12 hours. The ionic conductivity of the in-situ polymerized gel electrolyte was then tested. A Li / / Li symmetric cell was assembled, and the lithium-ion transference number was measured.

[0069] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room-temperature ionic conductivity of 5.3 × 10⁻⁶. -4 S / cm, lithium-ion transference number 0.71.

[0070] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2The surface density of the coating is adjusted, and the material is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, vacuum baked at 100°C for 48 hours, and then injected with the in-situ polymerized gel electrolyte precursor solution described in this embodiment. The mixture is then heated at 60°C for in-situ polymerization and sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0071] A full-cell test was conducted on the quasi-solid-state electrodeless lithium metal battery, and the first-cycle discharge specific capacity was 149.5 mAh g. -1 The initial coulombic efficiency was 90.23%; the coulombic efficiency was close to 100% during the cycle, and the capacity retention rate was still 67.29% after 300 cycles; after the first charge of the battery, the lithium deposition morphology on the current collector surface was dense, and no lithium dendrites were generated.

[0072] Example 3

[0073] In an argon-filled glove box, LiTFSI and LiPF6 are added to the additive shown in Formula II and the boron-containing in-situ polymerization monomer BOX-3, and the mixture is magnetically stirred for 10 minutes to obtain a clear in-situ polymerization gel electrolyte precursor solution; wherein the mass ratio of the boron-containing in-situ polymerization monomer BOX-3, the additive shown in Formula II, LiPF6, and LiTFSI is 79:3:16.5:1.5.

[0074] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and polymerized in the SL / / SL cell at 50°C for 4 hours. The ionic conductivity of the in-situ polymerized gel electrolyte was then tested. A Li / / Li symmetric cell was assembled, and the lithium-ion transference number was measured.

[0075] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room-temperature ionic conductivity of 2.7 × 10⁻⁶. -3 S / cm, lithium-ion transference number 0.78.

[0076] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2 The surface density of the coating is adjusted, and the material is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, vacuum baked at 100°C for 48 hours, and then injected with the in-situ polymerized gel electrolyte precursor solution described in this embodiment. In-situ polymerization is carried out at 70°C, and the mixture is sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0077] A quasi-solid-state lithium metal battery without a negative electrode was assembled using a lithium iron phosphate electrode as the counter electrode and a full-cell test was conducted. The battery's first-cycle discharge specific capacity was 159.5 mAh g. -1 The initial coulombic efficiency was 93.32%; the coulombic efficiency was close to 100% during the cycle, and the capacity retention rate was still 64.51% after 300 cycles; after the first charge of the battery, the lithium deposition morphology on the current collector surface was dense, and no lithium dendrites were generated.

[0078] Example 4

[0079] In an argon-filled glove box, LiPF6 is added to the additive shown in Formula II and the boron-containing in-situ polymerization monomer BOX-04, and the mixture is magnetically stirred for 10 minutes to obtain a clear in-situ polymerization gel electrolyte precursor solution; wherein the mass ratio of the boron-containing in-situ polymerization monomer BOX-4, the additive shown in Formula II, and LiPF6 is 79:3:18.

[0080] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and polymerized in the SL / / SL cell at 60°C for 4 hours. The ionic conductivity of the in-situ polymerized gel electrolyte was then measured. A Li / / Li symmetric cell was assembled, and the sodium ion transference number was measured.

[0081] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room-temperature ionic conductivity of 4.2 × 10⁻⁶. -3 S / cm, lithium-ion transference number 0.77.

[0082] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2 The surface density of the coating is adjusted, and the material is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, vacuum baked at 100°C for 48 hours, and then injected with the in-situ polymerized gel electrolyte precursor solution described in this embodiment. The mixture is then heated at 80°C for in-situ polymerization and sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0083] A quasi-solid-state lithium metal battery without a negative electrode was assembled using a lithium iron phosphate electrode as the counter electrode and a full-cell test was conducted. The battery's first-cycle discharge specific capacity was 149.5 mAh g. -1 The initial coulombic efficiency was 89.32%; the coulombic efficiency remained close to 100% throughout the cycle, and the capacity retention rate was still 60.38% after 300 cycles; after the first charge of the battery, the lithium deposition morphology on the current collector surface was dense, and no lithium dendrites were generated.

[0084] Comparative Example 1

[0085] In-situ polymerized gel electrolytes were prepared using the same method as in Example 1, except that the additives shown in Formula II were not added in Comparative Example 1, as detailed below:

[0086] In an argon-filled glove box, LiTFSI and LiPF6 were added to the boron-containing in-situ polymerization monomer BOX-1 and magnetically stirred for 10 min to obtain a clear in-situ polymerization gel electrolyte precursor solution; wherein the mass ratio of the boron-containing in-situ polymerization monomer BOX-1, LiPF6, and LiTFSI was 71.6:2.1:26.3.

[0087] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and polymerized in the SL / / SL battery at 80°C for 1 hour. The ionic conductivity of the in-situ polymerized gel electrolyte was then tested. A lithium-lithium symmetric battery was assembled, and the lithium-ion transference number was tested.

[0088] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room-temperature ionic conductivity of 8.9 × 10⁻⁶. -5 S / cm, lithium-ion transference number 0.63.

[0089] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2 The surface density of the coating is adjusted, and the material is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, and vacuum baked at 100°C for 48 hours. The in-situ polymerized gel electrolyte precursor solution described in this embodiment is then injected, and in-situ polymerization is carried out at 30°C. The mixture is then sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0090] A full-cell test was conducted on the quasi-solid-state electrodeless lithium metal battery, and the first-cycle discharge specific capacity was 139.5 mAh g. -1 The first cycle coulomb efficiency was 86.61%; after 300 cycles, the capacity retention rate was 53.3%.

[0091] A comparison of the experimental data from Comparative Example 1 and Example 1 shows that the conductivity of the prepared electrolyte decreases if the additive shown in Formula II is not added during the preparation of the in-situ polymerized gel electrolyte. This is because the dissociation degree of the conductive lithium salt is limited in the absence of the high-boiling-point additive shown in Formula II, which has good solubility for lithium salts, thus leading to a decrease in conductivity. This demonstrates that the addition of the additive can increase the solubility of the lithium salt while preventing the polymerization of Formula II from becoming too dense, which would reduce the lithium-ion transport capacity.

[0092] Comparative Example 2

[0093] The gel electrolyte was prepared using the same method as in Example 1, except that 1,3-dioxolane (DOL) was used instead of the boron-containing in-situ polymerization monomer BOX-1 provided in this invention, as detailed below:

[0094] In an argon-filled glove box, LiTFSI and LiPF6 are added to the additive shown in Formula II and 1,3-dioxolane, and the mixture is magnetically stirred for 10 min to obtain a clear in-situ polymerized gel electrolyte precursor solution; wherein the mass ratio of 1,3-dioxolane, the additive shown in Formula II, LiPF6, and LiTFSI is 63:10:2:25.

[0095] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and the SL / / SL battery was subjected to polymerization at 80°C for 1 hour. The ionic conductivity of the in-situ polymerized gel electrolyte was then tested. A lithium-lithium symmetric battery was assembled, and the lithium-ion transference number was tested.

[0096] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room-temperature ionic conductivity of 4.1 × 10⁻⁶. -4 S / cm, lithium-ion transference number 0.37.

[0097] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2 The surface density of the coating is adjusted, and the material is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, and vacuum baked at 100°C for 48 hours. The in-situ polymerized gel electrolyte precursor solution described in this embodiment is then injected, and in-situ polymerization is carried out at 30°C. The mixture is then sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0098] A full-cell test was conducted on the quasi-solid-state electrodeless lithium metal battery, and the first-cycle discharge specific capacity was 133.6 mAh g. -1 The first cycle coulomb efficiency was 80.93%; after 300 cycles, the capacity retention rate was 44.4%.

[0099] A comparison of the experimental data from Comparative Example 2 and Example 1 shows that when preparing gel electrolytes, replacing the boron-containing in-situ polymerized monomer provided by this invention with the traditional 1,3-dioxolane (DOL) results in a decrease in the lithium-ion transference number. Furthermore, the capacity retention rate decreases significantly with the increase in battery cycle count. This is because the polyether electrolyte formed by 1,3-dioxolane (DOL) has poor voltage resistance and is prone to decomposition during charge-discharge cycles.

[0100] The boron-containing in-situ polymerized monomer provided by this invention, through organic combination with the additive shown in Formula II, utilizes the complexing effect of electron-deficient boron atoms on conductive lithium salt anions to restrict anion migration, thereby increasing the degree of lithium salt dissociation and further improving lithium ion mobility, which can effectively reduce concentration polarization in secondary batteries. At the same time, in the presence of high-boiling-point fluorine-containing additives with good lithium salt solubility, the degree of lithium salt dissociation is fully released, greatly improving the stability of the electrolyte, broadening the battery's voltage resistance, and thus improving the battery's cycle performance.

[0101] Comparative Example 3

[0102] The gel electrolyte was prepared using the same method as in Example 1, except that BOX-1# was used instead of the boron-containing in-situ polymerizable monomer BOX-1 provided in this invention in this comparative example. The structural formula of BOX-1# is:

[0103]

[0104] Specifically as follows:

[0105] In an argon-filled glove box, LiTFSI and LiPF6 are added to the additive shown in Formula II and BOX-1#, and the mixture is magnetically stirred for 10 minutes to obtain a clear in-situ polymerized gel electrolyte precursor solution; wherein the mass ratio of BOX-1#, the additive shown in Formula II, LiPF6, and LiTFSI is 63:10:2:25.

[0106] The in-situ polymerized gel electrolyte precursor solution was injected into SL / / SL (SL being a stainless steel electrode), and the SL / / SL battery was subjected to polymerization at 80°C for 1 hour. The ionic conductivity of the in-situ polymerized gel electrolyte was then tested. A lithium-lithium symmetric battery was assembled, and the lithium-ion transference number was tested.

[0107] The prepared in-situ polymerized gel electrolyte for lithium-ion batteries has a room temperature ionic conductivity of 4.5 × 10⁻⁶. -4 S / cm, lithium-ion transference number 0.42.

[0108] Commercially available carbon-coated lithium iron phosphate was mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride in a weight ratio of 93:2:2:3. N-methylpyrrolidone was then added, and the mixture was stirred uniformly to prepare a positive electrode slurry. The slurry was prepared with a single-sided concentration of 27 mg / cm³. 2 The surface density of the coating is adjusted, and the material is vacuum dried at 100°C for 12 hours. Then, it is rolled and cut to form a positive electrode sheet; a copper foil current collector is used as the negative electrode sheet. The positive and negative electrode sheets are separated by a polypropylene (PP) ceramic separator, encapsulated in an aluminum-plastic film, and vacuum baked at 100°C for 48 hours. The in-situ polymerized gel electrolyte precursor solution described in this embodiment is then injected, and in-situ polymerization is carried out at 30°C. The mixture is then sealed to form a quasi-solid-state negative electrode-free lithium metal battery.

[0109] A full-cell test was conducted on the quasi-solid-state electrodeless lithium metal battery, and the first-cycle discharge specific capacity was 137.2 mAh g. -1 The first cycle coulomb efficiency was 82.78%; after 300 cycles, the capacity retention rate was 46.5%.

[0110] A comparison of the experimental data from Comparative Example 3 and Example 1 shows that using the boron-containing in-situ polymerized monomers described in this invention to prepare the gel electrolyte results in better application in batteries. Ethylene oxide ring structures are more prone to polymerization in the presence of lithium hexafluorophosphate, making it difficult to control the degree of polymerization. This results in an overly dense electrolyte, increasing the difficulty of lithium-ion transport and thus affecting the cycle performance of the battery cell.

[0111] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. An in-situ polymerized gel electrolyte, characterized in that, The in-situ polymerized gel electrolyte contains a boron-containing polymer monomer, the structural formula of which is shown in Formula I below: In Equation I, R1, R2, and R3 can be independently chosen from any of the following structural formulas: * indicates a connection site.

2. The in-situ polymerized gel electrolyte according to claim 1, characterized in that, The boron-containing polymer monomer is selected from at least one of the following structural formulas:

3. The in-situ polymerized gel electrolyte according to claim 1, characterized in that, The in-situ polymerized gel electrolyte comprises a conductive salt, an additive, and the boron-containing polymer monomer, wherein the additive is a fluorinated piperine compound.

4. The in-situ polymerized gel electrolyte according to claim 3, characterized in that, The in-situ polymerized gel electrolyte comprises, by weight, 13-30 parts of the conductive salt, 1-10 parts of the additive, and 55-85 parts of the boron-containing polymer monomer.

5. The in-situ polymerized gel electrolyte according to claim 3, characterized in that, The conductive salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, and lithium bis(fluorosulfonyl)imide.

6. The in-situ polymerized gel electrolyte according to claim 3, characterized in that, The additive is a compound of formula II as follows:

7. A method for preparing an in-situ polymerized gel electrolyte according to any one of claims 1-6, characterized in that, The preparation method is as follows: after uniformly mixing the conductive salt, additives and the boron-containing polymer monomer, an in-situ polymerized gel electrolyte precursor solution is obtained. The precursor solution is then subjected to a cross-linking in-situ polymerization reaction initiated by heating in a battery to obtain the in-situ polymerized gel electrolyte.

8. The method for preparing an in-situ polymerized gel electrolyte according to claim 7, characterized in that, The crosslinking polymerization reaction temperature is 30–80°C.

9. An application of an in-situ polymerized gel electrolyte according to any one of claims 1-6, characterized in that, The in-situ polymerized gel electrolyte is used in quasi-solid-state alkali metal secondary batteries.

10. The application of the in-situ polymerized gel electrolyte according to claim 9, characterized in that, The preparation method of the quasi-solid-state alkali metal secondary battery is as follows: after the conductive salt, additives and the boron-containing polymer monomer are mixed evenly, an in-situ polymerized gel electrolyte precursor solution is obtained. The precursor solution is injected between the positive and negative electrode plates of the assembled battery, and then in-situ ring-opening polymerization and solidification are achieved by heating to obtain an integrated quasi-solid-state alkali metal secondary battery.

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