A quasi-solid electrolyte system containing two-dimensional fluorophlogopite nanosheets and its application in secondary batteries

Abstract

The application discloses a kind of quasi-solid electrolyte systems containing two-dimensional fluorophlogopite nanosheet and its application in secondary battery.The quasi-solid electrolyte system has the mass fraction of 0.005% to 0.1% of exfoliated fluorophlogopite nanosheet dispersed in liquid base electrolyte, and cooperates with the use of separator coated with a composite coating containing the nanosheet.The nanosheet forms a thixotropic gel network with cations in the electrolyte through electrostatic interaction and coordination adsorption, migrates to the electrode microcrack through microscale convection during charging and discharging to produce bridging effect to inhibit volume expansion, while the separator coating uses the high aspect ratio of nanosheet to block metal dendrite penetration.The application is suitable for lithium ion batteries and sodium ion batteries, compatible with a variety of positive and negative electrode materials, significantly improves the cycle life, high voltage stability and safety performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a quasi-solid-state electrolyte system containing exfoliated fluorinated phlogopite nanosheets, a secondary battery comprising this electrolyte system, and a method for preparing the electrolyte system and the battery. This invention particularly relates to achieving interfacial stability, volume expansion suppression, and cycle life extension in lithium-ion and sodium-ion batteries by utilizing the physical bridging effect and chemical adsorption behavior of two-dimensional fluorinated phlogopite nanosheets at the electrode-electrolyte interface. Background Technology

[0002] During charge-discharge cycles, the active electrode materials in secondary batteries undergo lattice volume changes due to the insertion and extraction of lithium or sodium ions. For example, silicon anode materials experience a volume expansion rate exceeding 300% during lithium insertion, while layered oxide cathode materials exhibit a volume change rate of 10% to 15% during sodium ion extraction. These volume changes lead to microcracks in the electrode particles, mechanical separation at the electrode-electrolyte interface, and repeated rupture and regeneration of the solid electrolyte interface film. This continuously consumes active ions and increases the battery's internal resistance, ultimately resulting in capacity decay and shortened cycle life.

[0003] Furthermore, in high-voltage cathode material systems, the electrolyte undergoes oxidative decomposition on the cathode surface, causing transition metal ions to dissolve and deposit on the anode surface, further catalyzing electrolyte decomposition. In lithium or sodium anode systems, dendrite growth punctures the separator, leading to internal short circuits and posing safety risks.

[0004] In existing technologies, to alleviate the above problems, methods such as nano-sized electrode materials, surface coating with inert coatings, and optimization of the solid electrolyte interface film composition using electrolyte additives are commonly employed. However, a single method cannot simultaneously achieve high voltage stability on the positive electrode side, buffering of volume expansion on the negative electrode side, and puncture resistance of the separator. In particular, existing additives are mostly organic molecules or spherical inorganic nanoparticles, which have limited ability to dynamically fill microcracks in electrode particles and are insufficient in blocking two-dimensional lamellar dendrites.

[0005] Therefore, there is an urgent need for a universal technical solution that can improve the safety of the positive electrode interface, negative electrode interface and separator by using extremely low addition amounts and existing battery manufacturing processes. Summary of the Invention

[0006] The present invention aims to provide a quasi-solid-state electrolyte system containing two-dimensional fluorinated phlogopite nanosheets. This system disperses exfoliated fluorinated phlogopite nanosheets with specific morphology and surface charge characteristics in a conventional liquid electrolyte, and synergistically utilizes a separator coated with a composite coating containing these nanosheets. During battery charging and discharging, the nanosheets migrate to microcracks on the surface of the electrode active material particles via microscale convection and concentration gradient diffusion. Their two-dimensional rigidity creates a bridging effect, inhibiting crack propagation. Simultaneously, they capture transition metal ions through chemisorption and suppress electrolyte side reactions. Furthermore, the layered stacked coating of fluorinated phlogopite nanosheets on the separator surface significantly extends the penetration path of metal dendrites. This synergistic mechanism significantly extends battery cycle life, improves high-voltage stability and safety performance, without significantly increasing battery mass or volume, and without altering existing battery manufacturing equipment.

[0007] In a first aspect, the present invention provides a quasi-solid-state electrolyte system comprising: a liquid base electrolyte containing lithium salt or sodium salt and a non-aqueous organic solvent; exfoliated fluorophlogopite nanosheets dispersed in the liquid base electrolyte, wherein the average thickness of the fluorophlogopite nanosheets is 1 nm to 8 nm, the average lateral dimension is 50 nm to 500 nm, and the mass fraction of the fluorophlogopite nanosheets in the liquid base electrolyte is 0.005% to 0.1%; and a porous membrane disposed between the positive and negative electrodes of a secondary battery, wherein the surface of the porous membrane is coated with a composite coating comprising the fluorophlogopite nanosheets and inorganic ceramic particles; the surface of the exfoliated fluorophlogopite nanosheets carries a permanent negative charge, which, through electrostatic interaction and coordination adsorption of lithium ions or sodium ions at unsaturated sites at the edges, forms a weakly physical cross-linked network with ions and solvent molecules in the electrolyte, thereby endowing the electrolyte system with thixotropic gel characteristics, such that the viscosity of the quasi-solid-state electrolyte system at a shear rate of 0.1 s⁻¹ is greater than or equal to 50 mPa·s.

[0008] Furthermore, the lithium salt in the liquid basic electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonyl)imide; the sodium salt is selected from at least one of sodium hexafluorophosphate and sodium perchlorate.

[0009] Furthermore, the general chemical formula of the fluorinated phlogopite nanosheets is KMg3(AlSi3O4). 10 The Mg site can be partially replaced by Fe²⁺, and the F site can be partially replaced by OH⁻. This substitution is an isomorphous substitution phenomenon in natural fluorophlogopite minerals and does not affect the technical effect of this invention.

[0010] Furthermore, the mass fraction of fluorinated phlogopite nanosheets in the composite coating is 0.2% to 5%, and the thickness of the composite coating is 0.5 micrometers to 3 micrometers.

[0011] Secondly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and the quasi-solid-state electrolyte system described in the first aspect of the present invention.

[0012] Furthermore, the positive electrode comprises a positive electrode active material selected from any one of lithium iron phosphate, lithium manganese iron phosphate, lithium fluorophosphate, lithium vanadium phosphate, lithium-rich manganese-based positive electrode material, high-pressure spinel positive electrode material LiNi0.5Mn1.5O4, sulfur, sodium vanadium phosphate, Prussian blue analogue, sodium vanadium fluorophosphate, layered oxide sodium ion positive electrode material, polyanionic iron-based sodium ion positive electrode material, and sodium iron sulfate; the negative electrode comprises a negative electrode active material selected from any one of lithium titanate, sodium titanate, niobium titanium oxide, graphite, hard carbon, micron-sized silicon, silicon suboxide, tin phosphide, metallic lithium, metallic sodium, and organic carbonyl compounds.

[0013] Further, when the positive electrode active material is sulfur, the mass fraction of fluorinated phlogopite nanosheets in the quasi-solid-state electrolyte system is 0.05% to 0.1%; when the negative electrode active material is micron-sized silicon or silicon suboxide, the mass fraction of fluorinated phlogopite nanosheets in the quasi-solid-state electrolyte system is 0.02% to 0.08%; when the negative electrode active material is metallic lithium or metallic sodium, in the quasi-solid-state electrolyte system according to any one of claims 1 to 4, the mass fraction of fluorinated phlogopite nanosheets in the composite coating is 2% to 5%.

[0014] Thirdly, the present invention provides a method for preparing the quasi-solid-state electrolyte system described in the first aspect of the present invention, comprising the following steps: Step 1, crushing and purifying natural fluorite mica ore, dispersing it in deionized water, and using a sand mill at a speed of 2000 rpm to 3000 rpm for 2 to 6 hours to obtain a fluorite mica nanosheet suspension with an average thickness of 1 nanometer to 8 nanometers; Step 2, spray drying or freeze drying the fluorite mica nanosheet suspension to obtain powder; Step 3, adding the powder to a liquid basic electrolyte at a preset ratio, and ultrasonically dispersing for 30 to 60 minutes to obtain a quasi-solid-state electrolyte with thixotropic gel characteristics.

[0015] Fourthly, the present invention provides a method for preparing the secondary battery described in the second aspect of the present invention, comprising stacking or winding a positive electrode, a separator coated with a composite coating, and a negative electrode in sequence to form a cell, injecting it into the quasi-solid-state electrolyte system described in the first aspect of the present invention, and obtaining a finished secondary battery after encapsulation, formation, and aging.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. By introducing extremely low amounts (0.005% to 0.1%) of two-dimensional fluorophlogopite nanosheets into a liquid electrolyte, and utilizing their electrostatic interactions and coordination adsorption with lithium or sodium salt cations, a thixotropic gel network is formed without significantly increasing the viscosity of the system. This maintains the high ionic conductivity of the liquid electrolyte and endows the electrolyte system with quasi-solid-state properties that inhibit flow and block dendrites.

[0017] 2. Fluoropyramite nanosheets enter the tip of the microcracks in electrode particles through microscale convection and concentration gradient diffusion during battery charging and discharging. Their two-dimensional rigid structure creates a bridging effect on the two walls of the crack, effectively suppressing the pulverization and peeling of high-expansion electrode materials (such as silicon and layered oxides) during cycling, thereby reducing the rate of change of the macroscopic size of the electrode by more than 50%.

[0018] 3. The exposed Mg²⁺ and Al³⁺ unsaturated sites on the edges of the fluorophlogopite nanosheets constitute strong Lewis acid centers, which can efficiently capture fluoride ions generated by the decomposition of lithium salts in the electrolyte and transition metal ions dissolved from the positive electrode, inhibit the catalytic decomposition of the electrolyte under high voltage, and prevent the deposition and poisoning of transition metals on the negative electrode surface.

[0019] 4. The fluorinated phlogopite nanosheet composite coating on the diaphragm surface utilizes the high aspect ratio of two-dimensional nanosheets to form a layered, labyrinthine structure inside the coating, which greatly extends the piercing path of metal dendrites. At the same time, the inorganic ceramic particles in the coating ensure the thermal dimensional stability of the diaphragm, maintaining structural integrity during the 150-degree Celsius hot box test and preventing internal short circuits.

[0020] 5. The technical solution of this invention has extremely high versatility and is applicable to a variety of lithium-ion batteries and sodium-ion battery systems, including lithium iron phosphate, high-pressure spinel, lithium-rich manganese-based, sulfur cathode, micron-sized silicon, and metallic lithium sodium. Moreover, the preparation process is fully compatible with existing battery manufacturing lines and requires no additional equipment investment. Attached Figure Description

[0021] This instruction manual does not include any drawings. Detailed Implementation

[0022] The following 20 examples and 23 comparative examples illustrate in detail the specific embodiments of the present invention and its beneficial effects compared with the prior art. Unless otherwise specified, the performance tests of all examples and comparative examples were conducted under constant temperature environment of 25 degrees Celsius and constant voltage fixture of 3 MPa. Cyclic performance testing adopted constant current charge-discharge mode, and the number of cycles when the capacity retention rate dropped to 80% of the initial capacity was recorded. Safety tests included nail penetration test, overcharge test and 150 degrees Celsius hot box test. The macroscopic dimensional change rate of the positive electrode was calculated by measuring the difference in electrode thickness between the fully charged state and the uncharged state using an in-situ expansion tester. The amounts of each component are all parts by mass. The fluorinated phlogopite nanosheets used in the following examples were all prepared by sand milling and exfoliation method, and their general chemical formula is KMg3(AlSi3O) 10 F2, characterized by X-ray diffraction and atomic force microscopy, was found to have an average thickness in the range of 1 to 8 nanometers, a lateral dimension in the range of 50 to 500 nanometers, and a negative surface zeta potential in carbonate solvents. Example

[0023] This embodiment constructs a system using lithium titanate Li4Ti5O 12 This is a lithium-ion battery using lithium iron phosphate (LiFePO4) as the positive electrode active material and lithium iron phosphate as the negative electrode active material. The liquid electrolyte is a mixture of ethylene carbonate and dimethyl carbonate at a concentration of 1 mol / L lithium hexafluorophosphate. Exfoliated fluorophlogopite nanosheets with an average thickness of 3 nm, a lateral dimension of 150 nm, and a mass fraction of 0.01% are added to the electrolyte. Rheometer testing shows that this quasi-solid-state electrolyte has a viscosity of 62 mPa·s at a shear rate of 0.1 s⁻¹, exhibiting typical shear-thinning characteristics. The separator is a 7-micrometer-thick polyethylene film coated on both sides with a 1.5-micrometer-thick composite coating of boehmite and fluorophlogopite nanosheets, with the fluorophlogopite nanosheets comprising 1% of the coating by mass.

[0024] The resulting battery cell has a nominal voltage of 1.9 volts and a mass energy density of 142 watt-hours per kilogram. After 25,000 constant-current charge-discharge cycle tests at a 2 coulomb rate, the capacity retention was 80.2 percent. The macroscopic dimensional change rate of the positive electrode was 0.4 percent. No thermal runaway occurred during nail penetration testing, overcharge testing, and a 150°C hot box test. Example

[0025] This embodiment is basically the same as Embodiment 1, except that the positive electrode active material is replaced with lithium manganese iron phosphate (LiMn0.7Fe0.3PO4). The resulting cell has a mass energy density of 205 Wh / kg. After 21,000 cycles at a 2 coulomb rate, the capacity retention rate is 80.5%. The macroscopic size change rate of the positive electrode is 0.3%. Example

[0026] This embodiment is basically the same as Embodiment 1, except that the positive electrode active material is replaced with lithium iron fluorophosphate (LiFePO4F). The resulting cell has a mass energy density of 168 Wh / kg. After 19,000 cycles at a 2 coulomb rate, the capacity retention rate is 80.0%. Example

[0027] This embodiment is basically the same as Embodiment 1, except that the negative electrode active material is replaced with niobium titanium oxide (Nb). 16 W5O 55 The positive electrode active material is lithium manganese iron phosphate (LiMn0.7Fe0.3PO4). The resulting cell has a mass energy density of 192 Wh / kg. The capacity retention is 93% at a 10 coulomb rate and 80.3% after 18,000 cycles at a 2 coulomb rate. Example

[0028] This embodiment is basically the same as Example 1, except that the positive electrode active material is replaced with lithium vanadium phosphate Li3V2(PO4)3. The mass fraction of fluorinated phlogopite nanosheets in the electrolyte is 0.02%. The resulting cell has a mass energy density of 220 Wh / kg. After 17,000 cycles at a 2 coulomb rate, the capacity retention is 80.1%. Example

[0029] This embodiment constructs a sodium-ion battery using sodium titanate (Na2Ti3O7) as the negative electrode active material and sodium vanadium phosphate (Na3V2(PO4)2F3) as the positive electrode active material. The liquid base electrolyte is a propylene carbonate solution with 1 mol / L sodium chloride. Exfoliated fluorophlogopite nanosheets are added at a mass fraction of 0.015%. The fluorophlogopite mass fraction in the separator coating is 1%. The resulting cell has a mass energy density of 160 Wh / kg. Constant current charge-discharge cycle testing at 25°C and a coulomb rate of 2 resulted in a capacity retention of 80.2% after 22,000 cycles. Testing at -30°C showed a capacity retention of 56%. Example

[0030] This embodiment is essentially the same as Embodiment 6, except that the positive electrode active material is replaced with a Prussian blue analog Na2MnFe(CN)6, and a 5-nanometer-thick silver-doped fluorine-phlogopite layer is pre-coated on the surface of the positive electrode active material. The resulting cell has a mass energy density of 150 Wh / kg. After 15,000 cycles at 25°C and a rate of 5 coulombs, the capacity retention is 80.4 percent. Example

[0031] This embodiment is basically the same as Embodiment 6, except that the negative electrode active material is replaced with hard carbon, and the positive electrode active material is sodium vanadium fluorophosphate Na3V2(PO4)2F3. The mass fraction of fluorinated phlogopite nanosheets is 0.03%. The resulting cell has a mass energy density of 185 Wh / kg. After 4500 cycles at a rate of 2 coulombs, the capacity retention is 80.6%. Example

[0032] This embodiment is essentially the same as Embodiment 6, except that the positive electrode active material is replaced with a layered oxide NaNi1 / 3Fe1 / 3Mn1 / 3O2. The mass fraction of fluorine-phlogopite nanosheets is 0.025%. The macroscopic size change rate of the positive electrode is 1.7%. The resulting cell has a mass energy density of 205 Wh / kg. After 6000 cycles at a 2 coulomb rate, the capacity retention rate is 80.3%.

[0033] The mechanism behind the significant reduction in the macroscopic dimensional change rate of the cathode material is as follows: During the sodium removal process, the lattice of the layered oxide cathode material undergoes drastic expansion and contraction along the c-axis, resulting in a large number of intergranular cracks within the secondary particles. Fluoropyrite nanosheets dispersed in the electrolyte migrate to the crack tip region through microscale convection and concentration gradient diffusion. The exposed Mg²⁺ and Al³⁺ unsaturated sites at their edges form strong coordination bonds with oxygen atoms on the cathode material surface, creating nanoscale bridging between the crack walls. This prevents further crack propagation and particle peeling, thereby confining the macroscopic strain at the particle level within the range of elastic deformation of the secondary particles. Example

[0034] This embodiment is basically the same as Embodiment 6, except that the positive electrode active material is replaced with a polyanionic iron-based material, Na4Fe3(PO4)2P2O7. The resulting cell has a mass energy density of 125 Wh / kg. After 28,000 cycles at a 2 coulomb rate, the capacity retention rate is 80.0%. Example

[0035] This embodiment is basically the same as Embodiment 1, except that the positive electrode active material is replaced with lithium-rich manganese-based positive electrode material xLi2MnO3·(1-x)LiMO2, where M is nickel-cobalt-manganese. The mass fraction of fluorine-phlogopite nanosheets is 0.04%. The resulting cell has a mass energy density of 305 Wh / kg. After 2500 cycles at a 2 coulomb rate, the capacity retention is 80.2%. Example

[0036] This embodiment is essentially the same as Embodiment 1, except that the positive electrode active material is replaced with high-voltage spinel LiNi0.5Mn1.5O4. The liquid base electrolyte contains 0.05 mol / L lithium difluorooxalate borate as an additive. The mass fraction of fluorinated phlogopite nanosheets is 0.02%. The resulting cell has a mass energy density of 235 Wh / kg. After 12,000 cycles at a 2 coulomb rate, the capacity retention is 80.5%. No thermal runaway was observed during a 150°C hot box test. Example

[0037] This embodiment is essentially the same as Embodiment 1, except that the negative electrode active material is replaced with micron-sized silicon, and the mass fraction of fluorinated phlogopite nanosheets is 0.05%. The resulting cell has a mass energy density of 255 Wh / kg. The macroscopic size change rate of the negative electrode layer is 5%. After 800 cycles at a 2 coulomb rate, the capacity retention rate is 80.1%. Example

[0038] This embodiment is basically the same as Embodiment 13, except that the negative electrode active material is replaced with silicon suboxide (SiO2). x The positive electrode active material is lithium manganese iron phosphate (LiMn0.7Fe0.3PO4). The resulting cell has a mass energy density of 225 Wh / kg. The macroscopic size change rate of the negative electrode layer is 3%. After 2200 cycles at a 2 coulomb rate, the capacity retention rate is 80.3%. The initial coulomb efficiency is 82%. Example

[0039] This embodiment is essentially the same as Embodiment 1, except that the positive electrode active material is replaced with sulfur, and the mass fraction of fluorinated phlogopite nanosheets is 0.08%. The resulting cell has a mass energy density of 315 Wh / kg. The macroscopic size change rate of the positive electrode is less than 0.5%. After 1200 cycles at a 2 coulomb rate, the capacity retention rate is 80.4%. Example

[0040] This embodiment is essentially the same as Embodiment 6, except that the negative electrode active material is replaced with metallic sodium. The mass fraction of fluorinated phlogopite nanosheets in the separator coating is 3%. The resulting cell has a mass energy density of 345 Wh / kg. After 600 cycles at a current density of 0.5 mA / cm², the capacity retention is 80.2%, with no internal short circuits occurring. Example

[0041] This embodiment is essentially the same as Embodiment 6, except that the negative electrode active material is replaced with tin phosphide Sn4P3, and the positive electrode active material is the Prussian blue analog Na2MnFe(CN)6. The mass fraction of fluorine-phlogopite nanosheets is 0.04%. The macroscopic size change rate of the negative electrode layer is 6%. The resulting cell has a mass energy density of 235 Wh / kg. After 1200 cycles at a 2 coulomb rate, the capacity retention rate is 80.5%. Example

[0042] This embodiment is basically the same as Embodiment 6, except that the positive electrode active material is replaced with sodium ferric sulfate (Na2Fe2(SO4)3). The resulting cell has a mass energy density of 130 Wh / kg. After 18,000 cycles at a 2 coulomb rate, the capacity retention rate is 80.2 percent. Example

[0043] This embodiment is essentially the same as Embodiment 6, except that the positive electrode active material is replaced with selenium. The mass fraction of fluorine-phlogopite nanosheets is 0.06%. The resulting cell has a mass energy density of 215 Wh / kg. After 900 cycles at a 2 coulomb rate, the capacity retention is 80.3%. Example

[0044] This embodiment is basically the same as Example 6, except that the negative electrode active material is replaced with the organic carbonyl compound PTCDA, and the positive electrode active material is sodium vanadium phosphate Na3V2(PO4)2F3. The resulting cell has a mass energy density of 138 Wh / kg. After 15,000 cycles at a 2 coulomb rate, the capacity retention is 80.1 percent.

[0045] Comparative Example 1 This comparative example is essentially the same as Example 1, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte, and the separator coating is made of pure boehmite. The resulting cell, after 6000 cycles at a 2-coulomb rate, exhibited a capacity retention rate of 80% and thermal runaway during a needle penetration test.

[0046] Comparative Example 2 This comparative example is essentially the same as Example 2, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 8000 cycles at a 2 coulomb rate, the capacity retention rate drops to 80 percent.

[0047] Comparative Example 3 This comparative example is basically the same as Example 3, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 7000 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent.

[0048] Comparative Example 4 This comparative example is essentially the same as Example 4, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. At a 10 coulomb rate, the capacity retention is only 68 percent. After 6000 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent.

[0049] Comparative Example 5 This comparative example is essentially the same as Example 5, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 6500 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent.

[0050] Comparative Example 6 This comparative example is essentially the same as Example 6, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 7500 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent. At -30 degrees Celsius, the capacity retention is only 32 percent.

[0051] Comparative Example 7 This comparative example is essentially the same as Example 7, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 3500 cycles at a 5 coulomb rate, the capacity retention drops to 80 percent.

[0052] Comparative Example 8 This comparative example is essentially the same as Example 8, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 1200 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent.

[0053] Comparative Example 9 This comparative example is essentially the same as Example 9, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 1500 cycles at a 2 coulomb rate, the capacity retention rate drops to 80 percent. The macroscopic size change rate of the positive electrode reaches 11 percent.

[0054] Comparative Example 10 This comparative example is essentially the same as Example 10, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 12,000 cycles at a 2 coulomb rate, the capacity retention rate drops to 80 percent.

[0055] Comparative Example 11 This comparative example is essentially the same as Example 11, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 600 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent, and the voltage decays by 18 percent.

[0056] Comparative Example 12 This comparative example is essentially the same as Example 12, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 3000 cycles at a 2 coulomb rate, the capacity retention dropped to 80 percent. Thermal runaway occurred during testing in a 150°C hot box.

[0057] Comparative Example 13 This comparative example is essentially the same as Example 13, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 200 cycles at a 2 coulomb rate, the capacity retention rate drops to 80 percent. The macroscopic size change rate of the negative electrode layer reaches 18 percent.

[0058] Comparative Example 14 This comparative example is essentially the same as Example 14, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 500 cycles at a 2 coulomb rate, the capacity retention decreased to 80 percent. The initial coulombic efficiency was 72 percent.

[0059] Comparative Example 15 This comparative example is essentially the same as Example 15, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 150 cycles at a 2 coulomb rate, the capacity retention dropped to 80 percent, and severe polysulfide dissolution was detected by a UV-Vis spectrophotometer.

[0060] Comparative Example 16 This comparative example is essentially the same as Example 16, except that the diaphragm coating does not contain fluorinated phlogopite nanosheets. An internal short circuit occurred after 80 cycles at a current density of 0.5 mA / cm².

[0061] Comparative Example 17 This comparative example is essentially the same as Example 17, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 180 cycles at a 2 coulomb rate, the capacity retention rate drops to 80 percent.

[0062] Comparative Example 18 This comparative example is essentially the same as Example 18, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 6500 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent.

[0063] Comparative Example 19 This comparative example is essentially the same as Example 19, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 200 cycles at a 2 coulomb rate, the capacity retention drops to 80 percent.

[0064] Comparative Example 20 This comparative example is essentially the same as Example 20, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 5500 cycles at a 2 coulomb rate, the capacity retention rate drops to 80 percent.

[0065] Comparative Example 21 This comparative example is essentially the same as Example 1, except that the separator is an uncoated 7-micron-thick polyethylene film without a fluorinated phlogopite composite coating. The resulting cell exhibited a capacity retention of 80% after 12,000 cycles at a 2 coulomb rate. Compared to 25,000 cycles in Example 1, this demonstrates that the separator coating plays an indispensable role in interfacial stability at the end of long cycles.

[0066] Comparative Example 22 This comparative example is essentially the same as Example 1, except that fluorinated phlogopite nanosheets are not added to the liquid electrolyte. After 8000 cycles at a 2 coulomb rate, the capacity retention of the resulting cell decreased to 80% of its original value. Disassembly analysis revealed significant microcracks within the positive electrode particles, demonstrating that the free nanosheets dispersed in the electrolyte are essential for suppressing the propagation of bulk cracks in the electrode.

[0067] Comparative Example 23 This comparative example is essentially the same as Example 1, except that the two-dimensional fluorophlogopite nanosheets were replaced with an equal mass fraction of spherical fluorophlogopite powder with an average particle size of 200 nanometers. The resulting battery cell, after 5000 cycles at a 2 coulomb rate, showed a capacity retention rate of only 80%. This demonstrates that the high aspect ratio physical barrier and bridging effects resulting from the two-dimensional sheet-like morphology are key to the performance breakthrough of this invention, rather than merely the effect of the material's chemical composition.

[0068] A comparison of Examples 1 to 20 and Comparative Examples 1 to 23 clearly demonstrates that introducing extremely low amounts of exfoliated fluorophlogopite nanosheets into a liquid-based electrolyte, and using a separator coated with a composite coating containing these nanosheets, can significantly extend the cycle life of various positive and negative electrode material combinations, improve rate performance and safety, suppress microcrack propagation, transition metal dissolution, and volume expansion in the positive electrode material, and effectively prevent metal dendrite penetration. These effects have been verified in both lithium-ion and sodium-ion battery systems and are applicable to various combinations of zero-strain, low-strain, and high-expansion active materials.

[0069] Therefore, the quasi-solid-state electrolyte system and its application scheme provided by this invention achieve a universal improvement in the performance of existing secondary batteries with extremely simple process and extremely low cost, and have outstanding substantive features and significant progress.

Claims

1. A quasi-solid-state electrolyte system, characterized in that, The battery comprises: a liquid base electrolyte containing lithium or sodium salts and a non-aqueous organic solvent; exfoliated fluorophlogopite nanosheets dispersed in the liquid base electrolyte, wherein the average thickness of the fluorophlogopite nanosheets is 1 nm to 8 nm, the average lateral dimension is 50 nm to 500 nm, and the mass fraction of the fluorophlogopite nanosheets in the liquid base electrolyte is 0.005% to 0.1%; and a porous membrane disposed between the positive and negative electrodes of the secondary battery, wherein the surface of the porous membrane is coated with a composite coating comprising the fluorophlogopite nanosheets and inorganic ceramic particles; the surface of the exfoliated fluorophlogopite nanosheets carries a permanent negative charge, which forms a weak physical cross-linking network with ions and solvent molecules in the electrolyte through electrostatic interactions and coordination adsorption of lithium or sodium ions at edge unsaturated sites, such that the viscosity of the quasi-solid electrolyte system at a shear rate of 0.1 s⁻¹ is greater than or equal to 50 mPa·s.

2. The quasi-solid-state electrolyte system according to claim 1, characterized in that, The lithium salt in the liquid base electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonyl)imide; the sodium salt is selected from at least one of sodium hexafluorophosphate and sodium perchlorate.

3. The quasi-solid-state electrolyte system according to claim 1, characterized in that, The general chemical formula of the fluorophlogopite nanosheets is KMg3(AlSi3O4). 10 )F2, and the Mg site can be partially replaced by Fe²⁺, and the F site can be partially replaced by OH⁻.

4. The quasi-solid-state electrolyte system according to claim 1, characterized in that, The composite coating contains 0.2% to 5% fluorophlogopite nanosheets by mass, and the coating thickness is 0.5 micrometers to 3 micrometers.

5. A secondary battery comprising a positive electrode, a negative electrode, and a quasi-solid-state electrolyte system according to any one of claims 1 to 4.

6. The secondary battery according to claim 5, characterized in that, The positive electrode comprises a positive electrode active material selected from any one of lithium iron phosphate, lithium manganese iron phosphate, lithium fluorophosphate, lithium vanadium phosphate, lithium-rich manganese-based positive electrode material, high-pressure spinel positive electrode material LiNi0.5Mn1.5O4, sulfur, sodium vanadium phosphate, Prussian blue analogue, sodium vanadium fluorophosphate, layered oxide sodium ion positive electrode material, polyanionic iron-based sodium ion positive electrode material, and sodium iron sulfate; the negative electrode comprises a negative electrode active material selected from any one of lithium titanate, sodium titanate, niobium titanium oxide, graphite, hard carbon, micron-sized silicon, silicon suboxide, tin phosphide, metallic lithium, metallic sodium, and organic carbonyl compounds.

7. The secondary battery according to claim 6, characterized in that, When the positive electrode active material is sulfur, the mass fraction of fluorinated phlogopite nanosheets in the quasi-solid-state electrolyte system is 0.05% to 0.1%; when the negative electrode active material is micron-sized silicon or silicon suboxide, the mass fraction of fluorinated phlogopite nanosheets in the quasi-solid-state electrolyte system is 0.02% to 0.08%; when the negative electrode active material is metallic lithium or metallic sodium, in the quasi-solid-state electrolyte system according to any one of claims 1 to 4, the mass fraction of fluorinated phlogopite nanosheets in the composite coating is 2% to 5%.

8. A method for preparing the quasi-solid-state electrolyte system according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: After crushing and purifying the natural fluorinated phlogopite ore, disperse it in deionized water and peel it off using a sand mill at a speed of 2000 to 3000 rpm for 2 to 6 hours to obtain a suspension of fluorinated phlogopite nanosheets with an average thickness of 1 to 8 nanometers; Step 2: Spray dry or freeze dry the fluorinated phlogopite nanosheet suspension to obtain powder; Step 3: Add the powder to a liquid basic electrolyte at a preset ratio and ultrasonically disperse it for 30 to 60 minutes to obtain a quasi-solid electrolyte with thixotropic gel characteristics.

9. A method for preparing a secondary battery according to any one of claims 5 to 7, characterized in that, The method includes stacking or winding a positive electrode, a separator coated with a composite coating, and a negative electrode in sequence to form a battery cell, injecting it into a quasi-solid-state electrolyte system according to any one of claims 1 to 4, and then encapsulating, forming, and aging it to obtain a finished secondary battery.