A ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and a preparation method thereof

Abstract

The application provides a ceramic nanofiber heat insulation pad for lithium battery thermal runaway protection and a preparation method thereof, and belongs to the technical field of lithium battery thermal runaway protection. The heat insulation pad introduces stepped heat absorption particles and bridging composite micropowder into the inorganic fiber framework to form multi-stage synergistic protection in different temperature zones. The inorganic heat absorption core in the stepped heat absorption particles decomposes in multiple stages to continuously absorb heat in a wide temperature range of about 220-550 DEG C, and the boron nitride nanosheet on the surface helps to produce certain in-plane heat diffusion in the local micro area. The glass powder in the bridging composite micropowder softens at about 500-700 DEG C, and then forms a discrete liquid phase bridge at the fiber node to enhance the structural integrity. The surface-embedded nanometer metal oxide particles and the glass bridge form a local infrared extinction area together, which helps to inhibit the radiation heat transfer at the high temperature stage. The two types of particles relay the temperature zone, and cooperate with the double-scale fiber framework to inhibit the gas phase heat conduction, so as to perform graded heat insulation protection in the thermal runaway process.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery thermal runaway protection technology, and relates to a ceramic nanofiber heat insulation pad for lithium battery thermal runaway protection and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles and large-scale energy storage systems, the safety of battery modules has become an increasingly important concern. Lithium-ion batteries may enter a state of thermal runaway when subjected to abnormal operating conditions such as internal short circuits, overcharging, or external heating: the cell temperature rises sharply in a short period of time, accompanied by the ejection of large amounts of high-temperature, high-pressure flammable gas. If the heat cannot be effectively isolated after thermal runaway occurs in one cell within the module, adjacent cells will be heated to the trigger temperature, causing the thermal runaway to spread and potentially leading to a fire or even an explosion of the entire battery pack. Therefore, placing thermal insulation pads between adjacent cells is a commonly used thermal protection measure in current battery module designs.

[0003] Currently, the thermal insulation materials used in battery modules mainly fall into the following categories: The first category is aerogel composite thermal insulation materials, represented by silica aerogel impregnated inorganic fiber felt. These materials utilize the nanoporous structure of aerogel to reduce gas phase heat conduction and convective heat transfer. However, aerogels are prone to sintering shrinkage at high temperatures, and their production costs are relatively high. The second category consists of thermal insulation sheets that incorporate conventional inorganic heat-absorbing components such as aluminum hydroxide and magnesium hydroxide into a ceramic fiber matrix. These sheets utilize endothermic decomposition reactions to consume some of the heat. However, the decomposition temperature range of these conventional heat-absorbing components is concentrated, and the heat absorption window is narrow. Furthermore, a large number of related patents have formed a relatively dense technological layout. The third category is multi-layer thermal barrier structures containing an inflatable flame-retardant layer. These structures achieve thermal insulation and gap filling through the foaming of an organic expansion system upon exposure to fire. However, the stability and residual structural strength of the organic matrix at sustained high temperatures are often insufficient. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The thermal insulation pad incorporates two types of functional particles—stepped heat-absorbing particles and bridging composite microparticles—into an inorganic fiber skeleton. During thermal runaway, these particles respond sequentially at different temperature ranges: the inorganic heat-absorbing core in the stepped heat-absorbing particles undergoes multi-stage decomposition within a wide temperature range of approximately 220-550℃, continuously consuming heat to delay temperature transfer; the boron nitride nanosheets attached to its surface contribute to a certain degree of in-plane thermal diffusion tendency at the local micro-region level; the glass powder in the bridging composite microparticles softens at approximately 500-700℃ and forms discrete liquid-phase bridging at fiber intersections, enhancing structural integrity at high temperatures. Simultaneously, the high-refractive-index nano-metal oxide particles pre-composite to the glass powder surface facilitate the formation of local infrared extinction regions with the glass bridging phase, thereby suppressing radiative heat transfer during high-temperature stages to a certain extent. Two types of functional particles form a multi-level synergistic protection mechanism through temperature zone relay: "medium-temperature stepped heat absorption - high-temperature bridging reinforcement - high-temperature infrared extinction." Combined with the dual-scale fiber skeleton's suppression of gas-phase thermal conductivity, this facilitates continuous graded thermal insulation protection during thermal runaway. The thermal insulation pad is manufactured using a wet papermaking process, is compatible with papermaking equipment, and is suitable for thermal runaway protection between adjacent cells in lithium battery modules.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection, the method comprising:

[0007] S1: Hydrated basic magnesium carbonate powder and boron nitride nanosheets were mixed and dispersed in a mixed solvent, silane coupling agent KH-560 was added, mechanically stirred, and then the concentrated slurry was obtained by rotary evaporation under reduced pressure. The slurry was then immersed in cationic polydiallyldimethylammonium chloride aqueous solution for treatment, then filtered, washed with deionized water, and vacuum dried to obtain stepped endothermic particles.

[0008] S2: Zinc oxide, boron oxide, silicon dioxide, and aluminum oxide are mixed and placed in a crucible, heated and kept at a temperature in a muffle furnace until melted. The melt is then quickly poured into deionized water for water quenching to obtain glass fragments. The glass fragments are dried and then wet-milled in a planetary ball mill using anhydrous ethanol as the wet grinding medium. After drying and sieving, zinc borosilicate glass powder is obtained. This powder is then mixed with nano-titanium dioxide and ball-milled in a planetary ball mill without grinding balls. Finally, it is sieved to obtain bridged composite micro powder.

[0009] S3: Add deionized water to a pulper, add mullite chopped fibers for shearing and pulping; add alumina fibers for further dispersion, add colloidal silica dropwise, stir, add stepped endothermic particles and stir, add bridging composite micro powder and stir, add aramid precipitated fibers, then adjust the pH with sodium hydroxide solution, add cationic polyacrylamide solution, and stir to obtain wet papermaking pulp;

[0010] S4: The wet-processed pulp is poured into a fourdrinier paper machine and dewatered under negative pressure to obtain wet fiber felt; the wet felt is transferred to a hot press dryer for segmented drying: the first stage is heat preservation without external pressure; the second stage is heat preservation after applying a second pressure; the third stage is heat preservation after maintaining the second pressure; after the process is completed, the pressure is released and the material is naturally cooled with the furnace to obtain a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection.

[0011] As a preferred technical solution of the present invention, in step S1, the D50 particle size of the hydrated basic magnesium carbonate powder is 5-20 μm, for example, it can be 5.0 μm, 6.5 μm, 8.0 μm, 9.5 μm, 11.0 μm, 12.5 μm, 14.0 μm, 15.5 μm, 17.0 μm, 18.5 μm or 20.0 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] In some optional embodiments, the mass ratio of the hydrated basic magnesium carbonate powder to the boron nitride nanosheets is (5-15):1, for example, it can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1 or 15:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0013] In some optional embodiments, the volume ratio of deionized water to ethanol in the mixed solvent is (2-5):(98-95), for example, it can be (2.0, 2.3, 2.6, 2.9, 3.2, 3.5, 3.8, 4.1, 4.4, 4.7 or 5.0):(98.0, 97.7, 97.4, 97.1, 96.8, 96.5, 96.2, 95.9, 95.6, 95.3 or 95.0), but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the total mass ratio of the hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of the mixed solvent is 1g:(5-10)mL, for example, it can be 1g:5.0mL, 1g:5.5mL, 1g:6.0mL, 1g:6.5mL, 1g:7.0mL, 1g:7.5mL, 1g:8.0mL, 1g:8.5mL, 1g:9.0mL, 1g:9.5mL or 1g:10.0mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, the amount of silane coupling agent KH-560 added is 1-3% of the total mass of hydrated basic magnesium carbonate and boron nitride, for example, it can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8% or 3.0%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the temperature of the mechanical stirring is 40-60°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0017] In some alternative embodiments, the mechanical stirring time is 2-4 hours, for example, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0018] In some optional embodiments, the temperature of the vacuum rotary evaporation is 50-60°C, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0019] In some optional embodiments, the pressure of the reduced-pressure rotary evaporation is -0.08 to -0.1 MPa, for example, it can be -0.100 MPa, -0.098 MPa, -0.096 MPa, -0.094 MPa, -0.092 MPa, -0.090 MPa, -0.088 MPa, -0.086 MPa, -0.084 MPa, -0.082 MPa or -0.080 MPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the volume of the concentrated slurry is 1 / 5 to 1 / 3 of the original volume, for example, it can be 1 / 5.0, 1 / 4.8, 1 / 4.6, 1 / 4.4, 1 / 4.2, 1 / 4.0, 1 / 3.8, 1 / 3.6, 1 / 3.4, 1 / 3.2 or 1 / 3.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] In some optional embodiments, the concentration of the cationic polydiallyldimethylammonium chloride aqueous solution is 1-3 mg / mL, for example, it can be 1.0 mg / mL, 1.2 mg / mL, 1.4 mg / mL, 1.6 mg / mL, 1.8 mg / mL, 2.0 mg / mL, 2.2 mg / mL, 2.4 mg / mL, 2.6 mg / mL, 2.8 mg / mL or 3.0 mg / mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the processing time is 20-40 minutes, for example, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes or 40 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the total mass ratio of the hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of the cationic polydiallyldimethylammonium chloride aqueous solution is 1g:(10-20)mL, for example, it can be 1g:10mL, 1g:11mL, 1g:12mL, 1g:13mL, 1g:14mL, 1g:15mL, 1g:16mL, 1g:17mL, 1g:18mL, 1g:19mL or 1g:20mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] The conductivity of the filtrate after washing is less than 50 μS / cm.

[0025] In some optional embodiments, the vacuum drying temperature is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] In some optional embodiments, the vacuum drying time is 4-8 hours, for example, 4.0 hours, 4.4 hours, 4.8 hours, 5.2 hours, 5.6 hours, 6.0 hours, 6.4 hours, 6.8 hours, 7.2 hours, 7.6 hours or 8.0 hours, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] As a preferred technical solution of the present invention, in step S2, the mass ratio of zinc oxide, boron oxide, silicon dioxide and aluminum oxide is (35-45):(25-35):(15-25):(2-6), for example, it can be (35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45):(25, 26, 27, 28, 29, 30, 31, 32, 33, 34 or 35):(15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25):(2.0, 2.4, 2.8, 3.2, 3.6, 4.0, 4.4, 4.8, 5.2, 5.6 or 6.0), but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] In some alternative embodiments, the heating rate is 5-10°C / min, for example, it can be 5.0°C / min, 5.5°C / min, 6.0°C / min, 6.5°C / min, 7.0°C / min, 7.5°C / min, 8.0°C / min, 8.5°C / min, 9.0°C / min, 9.5°C / min or 10.0°C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some optional embodiments, the temperature of the heat preservation melting is 1150-1350°C, for example, it can be 1150°C, 1170°C, 1190°C, 1210°C, 1230°C, 1250°C, 1270°C, 1290°C, 1310°C, 1330°C or 1350°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the heat preservation and melting time is 1-2 hours, for example, it can be 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the wet grinding ball mass ratio of the glass shards is (3-5):1, for example, it can be 3.0:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4.0:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1 or 5.0:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the wet grinding speed of the glass shards is 300-500 rpm, for example, it can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm or 500 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the wet grinding time of the glass fragments is 2-4 hours, for example, it can be 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the D50 particle size of the zinc borosilicate glass powder is 5-15 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] In some optional embodiments, the mass ratio of zinc borosilicate glass powder to nano titanium dioxide is (10-20):1, for example, it can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the ball milling speed after mixing the zinc borosilicate glass powder with nano titanium dioxide is 1500-3000 rpm, for example, it can be 1500 rpm, 1650 rpm, 1800 rpm, 1950 rpm, 2100 rpm, 2250 rpm, 2400 rpm, 2550 rpm, 2700 rpm, 2850 rpm or 3000 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] In some optional embodiments, the ball milling time after mixing the zinc borosilicate glass powder with nano titanium dioxide is 15-30 min, for example, it can be 15.0 min, 16.5 min, 18.0 min, 19.5 min, 21.0 min, 22.5 min, 24.0 min, 25.5 min, 27.0 min, 28.5 min or 30.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0038] In some optional embodiments, the D50 particle size of the bridging composite micropowder is 10-20 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] As a preferred technical solution of the present invention, in step S3, the rotation speed of the shearing and pulping is 1000-2000 rpm, for example, it can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm or 2000 rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] In some optional embodiments, the shearing and pulping time is 2-5 min, for example, it can be 2.0 min, 2.3 min, 2.6 min, 2.9 min, 3.2 min, 3.5 min, 3.8 min, 4.1 min, 4.4 min, 4.7 min or 5.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0041] In some alternative embodiments, the diameter of the alumina fiber is 0.3-3 μm, for example, it can be 0.30 μm, 0.57 μm, 0.84 μm, 1.11 μm, 1.38 μm, 1.65 μm, 1.92 μm, 2.19 μm, 2.46 μm, 2.73 μm or 3.00 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] In some optional embodiments, the rotation speed at which the alumina fibers continue to disperse after addition is 800-1200 rpm, for example, 800 rpm, 840 rpm, 880 rpm, 920 rpm, 960 rpm, 1000 rpm, 1040 rpm, 1080 rpm, 1120 rpm, 1160 rpm or 1200 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0043] In some optional embodiments, the dispersion time after the addition of alumina fibers is 1-3 min, for example, it can be 1.0 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2.0 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min or 3.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0044] In some optional embodiments, the stirring speed after adding colloidal silica is 500-800 rpm, for example, 500 rpm, 530 rpm, 560 rpm, 590 rpm, 620 rpm, 650 rpm, 680 rpm, 710 rpm, 740 rpm, 770 rpm or 800 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] In some optional embodiments, the stirring time after adding colloidal silica is 3-5 min, for example, it can be 3.0 min, 3.2 min, 3.4 min, 3.6 min, 3.8 min, 4.0 min, 4.2 min, 4.4 min, 4.6 min, 4.8 min or 5.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] In some optional embodiments, the stirring time after adding the stepped endothermic particles is 5-10 min, for example, it can be 5.0 min, 5.5 min, 6.0 min, 6.5 min, 7.0 min, 7.5 min, 8.0 min, 8.5 min, 9.0 min, 9.5 min or 10.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0047] In some optional embodiments, the stirring time after adding the bridging composite micro powder is 3-5 min, for example, it can be 3.0 min, 3.2 min, 3.4 min, 3.6 min, 3.8 min, 4.0 min, 4.2 min, 4.4 min, 4.6 min, 4.8 min or 5.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0048] In some optional embodiments, the concentration of the sodium hydroxide solution is 0.5-1 mol / L, for example, it can be 0.50 mol / L, 0.55 mol / L, 0.60 mol / L, 0.65 mol / L, 0.70 mol / L, 0.75 mol / L, 0.80 mol / L, 0.85 mol / L, 0.90 mol / L, 0.95 mol / L or 1.00 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In some alternative embodiments, the pH is adjusted to 7.5-9.0 after the addition of aramid precipitated fibers. For example, the pH can be adjusted to 7.50, 7.65, 7.80, 7.95, 8.10, 8.25, 8.40, 8.55, 8.70, 8.85 or 9.00, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] In some optional embodiments, the stirring time after adding the cationic polyacrylamide solution is 2-5 min, for example, 2.0 min, 2.3 min, 2.6 min, 2.9 min, 3.2 min, 3.5 min, 3.8 min, 4.1 min, 4.4 min, 4.7 min or 5.0 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0051] In some optional embodiments, the solid content of the wet papermaking slurry is 0.1-0.5 wt.%, for example, it can be 0.10 wt.%, 0.14 wt.%, 0.18 wt.%, 0.22 wt.%, 0.26 wt.%, 0.30 wt.%, 0.34 wt.%, 0.38 wt.%, 0.42 wt.%, 0.46 wt.%, or 0.50 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0052] In some optional embodiments, the content of colloidal silica (calculated as SiO2 dry solids) in the total dry solids of the wet papermaking slurry is 1.5-4 wt%, for example, it can be 1.50 wt%, 1.75 wt%, 2.00 wt%, 2.25 wt%, 2.50 wt%, 2.75 wt%, 3.00 wt%, 3.25 wt%, 3.50 wt%, 3.75 wt%, or 4.00 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] In some optional embodiments, the content of stepped endothermic particles in the total dry solids of the wet papermaking slurry is 4-8 wt%, for example, it can be 4.0 wt%, 4.4 wt%, 4.8 wt%, 5.2 wt.%, 5.6 wt.%, 6.0 wt.%, 6.4 wt.%, 6.8 wt.%, 7.2 wt.%, 7.6 wt.%, or 8.0 wt.%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0054] In some optional embodiments, the content of bridging composite micro powder in the total dry solids of the wet papermaking slurry is 2-6 wt%, for example, it can be 2.0 wt%, 2.4 wt.%, 2.8 wt.%, 3.2 wt.%, 3.6 wt.%, 4.0 wt.%, 4.4 wt.%, 4.8 wt.%, 5.2 wt.%, 5.6 wt.%, or 6.0 wt.%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0055] In some optional embodiments, the content of aramid precipitated fibers in the total dry solids of the wet papermaking slurry is 0.2-1.5 wt%, for example, it can be 0.20 wt%, 0.33 wt%, 0.46 wt%, 0.59 wt%, 0.72 wt%, 0.85 wt%, 0.98 wt%, 1.11 wt%, 1.24 wt%, 1.37 wt%, or 1.50 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0056] In some optional embodiments, the mass ratio of mullite chopped fibers to alumina fibers in the inorganic fiber skeleton is (75-95):(25-5), for example, it can be (75, 77, 79, 81, 83, 85, 87, 89, 91, 93 or 95):(25, 23, 21, 19, 17, 15, 13, 11, 9, 7 or 5), but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0057] In some optional embodiments, the concentration of the cationic polyacrylamide solution is 0.05-0.1 wt.%, for example, it may be 0.05 wt.%, 0.055 wt.%, 0.06 wt.%, 0.065 wt.%, 0.07 wt.%, 0.075 wt.%, 0.08 wt.%, 0.05 wt.%, 0.09 wt.%, 0.095 wt.%, or 0.1 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0058] In some optional embodiments, the cationic polyacrylamide solution accounts for 0.01-0.05% of the total dry solids mass of the wet papermaking slurry, for example, 0.010%, 0.014%, 0.018%, 0.022%, 0.026%, 0.030%, 0.034%, 0.038%, 0.042%, 0.046%, or 0.050%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0059] As a preferred technical solution of the present invention, in step S4, the pressure of the negative pressure filtration is -0.03 to -0.06 MPa, for example, it can be -0.060 MPa, -0.057 MPa, -0.054 MPa, -0.051 MPa, -0.048 MPa, -0.045 MPa, -0.042 MPa, -0.039 MPa, -0.036 MPa, -0.033 MPa or -0.030 MPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0060] In some optional embodiments, the negative pressure filtration time is 1-3 min, for example, it can be 1.0 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2.0 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min or 3.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0061] In some alternative embodiments, the drying temperature of the first stage is 80-100°C, for example, it can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0062] In some optional embodiments, the heating rate of the first stage is 1-3℃ / min, for example, 1℃ / min, 1.2℃ / min, 1.4℃ / min, 1.6℃ / min, 1.8℃ / min, 2℃ / min, 2.2℃ / min, 2.4℃ / min, 2.6℃ / min, 2.8℃ / min or 3℃ / min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0063] In some optional embodiments, the heat preservation time for the first stage of drying is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0064] In some alternative embodiments, the pressure applied in the second stage is 0.02-0.05 MPa, for example, 0.020 MPa, 0.023 MPa, 0.026 MPa, 0.029 MPa, 0.032 MPa, 0.035 MPa, 0.038 MPa, 0.041 MPa, 0.044 MPa, 0.047 MPa or 0.050 MPa, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0065] In some optional embodiments, the heating rate of the second stage is 0.5-2℃ / min, for example, it can be 0.5℃ / min, 0.8℃ / min, 1℃ / min, 1.1℃ / min, 1.2℃ / min, 1.3℃ / min, 1.4℃ / min, 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min or 2℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0066] In some optional embodiments, the drying temperature of the second stage is 120-140°C, for example, 120°C, 122°C, 124°C, 126°C, 128°C, 130°C, 132°C, 134°C, 136°C, 138°C or 140°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0067] In some optional embodiments, the heat preservation time for the second stage drying is 60-120 min, for example, it can be 60 min, 66 min, 72 min, 78 min, 84 min, 90 min, 96 min, 102 min, 108 min, 114 min or 120 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0068] In some optional embodiments, the heating rate of the third stage is 0.5-2℃ / min, for example, it can be 0.5℃ / min, 0.8℃ / min, 1℃ / min, 1.1℃ / min, 1.2℃ / min, 1.3℃ / min, 1.4℃ / min, 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min or 2℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0069] In some optional embodiments, the temperature of the third stage is 150-180°C, for example, it can be 150°C, 153°C, 156°C, 159°C, 162°C, 165°C, 168°C, 171°C, 174°C, 177°C or 180°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0070] In some optional embodiments, the heat preservation time of the third stage is 30-60 minutes, for example, it can be 30 minutes, 33 minutes, 36 minutes, 39 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 51 minutes, 54 minutes, 57 minutes or 60 minutes, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0071] In a second aspect, the present invention provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection, which is prepared according to the preparation method described in the first aspect.

[0072] When subjected to thermal runaway thermal shock, the thermal insulation pad of the present invention has two types of functional particles responding sequentially in different temperature zones, forming a multi-level protection mechanism in synergy with the inorganic fiber skeleton.

[0073] In the initial to intermediate temperature stages of thermal runaway, the inorganic endothermic nuclei within the stepped endothermic particles undergo a progressive thermal decomposition reaction. The thermal decomposition of hydrated basic magnesium carbonate occurs in stages over a wide temperature range from approximately 220°C to approximately 550°C: first, a water of crystallization removal reaction occurs near 220-300°C; then, a structural hydroxyl group removal reaction occurs in the 350-400°C range; and finally, a carbonate decomposition reaction occurs in the 450-550°C range, releasing CO2. All three stages of decomposition are endothermic processes, continuously consuming heat over a wide temperature range, which helps to slow down the temperature transfer rate across the insulation pad. Compared to endothermic materials that decompose at a single temperature point, this stepped decomposition characteristic allows the endothermic effect to persist longer during the thermal runaway process. Simultaneously, the H2O and CO2 released during the decomposition process are both non-flammable gases. These gases, after escaping from the particles, can cause a certain degree of disturbance to the flammable atmosphere in the pore space of the insulation pad.

[0074] In the stepped endothermic particles, boron nitride nanosheets attached to the surface of the inorganic endothermic core also play a certain auxiliary role in this temperature range. Boron nitride has high in-plane thermal conductivity. During the wet papermaking and dehydration process, these layered particles tend to align along the plane of the insulation pad under the action of fluid shear force. This orientation feature helps to generate a certain degree of in-plane heat diffusion at the local micro-area level, thereby promoting the dispersion of heat in the planar direction and reducing the tendency of local heat concentration to be transferred along the thickness direction. Since the boron nitride nanosheets are attached to the core surface in a discontinuous semi-encapsulated form and have a low content in the insulation pad, they cannot form a continuous heat-conducting network that runs through the entire plane of the insulation pad. The above-mentioned in-plane heat diffusion effect is mainly reflected in the local micro-area where the particles are located. At the same time, this discontinuous semi-encapsulated structure retains sufficient gaps on the core surface to ensure that the gas generated during the thermal decomposition of the core can escape smoothly without being hindered by the outer coating and affecting the endothermic reaction process.

[0075] When the temperature rises further to approximately 500-700℃, the endothermic decomposition of the stepped heat-absorbing particles is essentially complete, and the insulation pad enters a high-temperature stage dominated by bridging composite micropowder. Within this temperature range, the glass powder in the bridging composite micropowder reaches its softening temperature and begins to transform from a solid to a viscous flow state. Driven by surface tension and capillary force, the softened glass liquid wets and flows along the fiber surface, facilitating the formation of discrete liquid-phase bridging at some adjacent fiber intersections. After these liquid-phase bridgings solidify at high temperatures, they transform the fiber network, originally connected only by physical entanglement and sol-gel bonding, into a reinforced structure with rigid connection nodes. This enhances the structural integrity of the insulation pad under high-temperature airflow and inhibits fiber pulverization and scattering. Because the total content of glass powder in the insulation pad is controlled within the range of 2-6 wt%, its volume is limited, and the formed liquid-phase bridging is discretely distributed, covering only some fiber intersections rather than sintering the entire fiber network into a unified, dense ceramic. This discrete bridging method reinforces local nodes while preserving the overall porous structure and a certain degree of flexibility of the fiber network.

[0076] Another function of the bridging composite micropowder lies in its ability to suppress high-temperature radiative heat transfer through nano-metal oxide particles. When temperatures exceed approximately 600°C, thermal radiation gradually becomes the primary mode of heat transfer in porous fiber insulation materials. Nano-metal oxide particles, pre-embedded in the shallow layer of glass powder via dry mechanical composite bonding, can co-distribute with the softened glass bridging phase in the localized bridging region. These high-refractive-index nanoparticles help improve the extinction capacity of the localized region against mid- and far-infrared thermal radiation, thus mitigating radiative heat transfer at high temperatures to some extent.

[0077] At the fiber skeleton level, the thermal insulation pad employs a dual-scale composite structure of chopped mullite fibers and alumina fibers. The chopped mullite fibers form the main skeleton of the pad, providing macroscopic thickness and sufficient porosity; alumina fibers are interspersed within the spaces formed by the coarse fibers, reducing the equivalent pore size of the fiber network. This reduction in pore size helps suppress natural convection of air within the pores and gas-phase heat transfer, thereby lowering the equivalent thermal conductivity of the insulation pad in the medium- and low-temperature range. Regarding the bonding system, colloidal silica undergoes a dehydration condensation reaction during drying to form an inorganic silica network, providing inorganic bonding at fiber intersections and maintaining basic connection strength at high temperatures; a small amount of aramid precipitated fibers utilize their high specific surface area to form physical entanglement between fibers, providing wet-sheet forming strength and operational flexibility under normal and medium-low temperature conditions.

[0078] This invention first prepares functional particles separately, and then uses a wet papermaking process to composite them. This process design decouples the preparation temperature of the functional particles from the molding temperature of the thermal insulation pad: the preparation of the stepped heat-absorbing particles is completed under low-temperature conditions, avoiding the problem of premature decomposition of the heat-absorbing core due to high-temperature treatment; although the glass powder in the bridging composite micropowder is prepared by high-temperature melting, its subsequent composite process with nano-metal oxides and the final papermaking are all carried out at low temperatures, ensuring the structural integrity of each functional component. During the slurry preparation process, colloidal silica is added before the stepped heat-absorbing particles, allowing it to pre-adsorb onto the fiber surface, preventing the subsequently added cationic modified stepped heat-absorbing particles from preferentially adsorbing the inorganic sol, thus facilitating the pre-formation of an adsorption layer of inorganic sol on the fiber surface. In the segmented heating and drying process after papermaking, the maximum temperature is controlled below 180℃, lower than the dehydration initiation temperature of hydrated basic magnesium carbonate, ensuring that the stepped heat-absorbing particles maintain their complete heat absorption potential in the finished thermal insulation pad.

[0079] This application utilizes the temperature zone relay of stepped heat-absorbing particles and bridging composite micropowders, combined with the porosity regulation effect of the dual-scale fiber skeleton, to facilitate the formation of a graded protection mechanism during thermal runaway, which includes intermediate-temperature heat-absorbing buffer, high-temperature discrete bridging reinforcement, and synergistic effect of local infrared extinction.

[0080] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0081] This invention introduces two types of functional particles—step-endothermic particles and bridging composite micropowder—into an inorganic fiber skeleton. By utilizing the sequential response characteristics of these two particles in different temperature zones, a graded synergistic protection mechanism is formed, which is dominated by step-endothermic processes in the mid-temperature stage and by liquid-phase bridging reinforcement and infrared extinction in the high-temperature stage. This mechanism is beneficial for continuously providing thermal insulation and protection during thermal runaway.

[0082] The stepped heat-absorbing particles of the present invention adopt an inorganic heat-absorbing core with multi-stage decomposition characteristics. Its thermal decomposition process is carried out in stages within a wide temperature range of about 220-550°C. Compared with conventional heat-absorbing materials that decompose at a single temperature point, it is beneficial to continuously consume heat over a wider temperature range and delay the temperature transfer on both sides of the heat insulation pad.

[0083] In the bridging composite micro powder of the present invention, the glass powder softens at high temperature and forms discrete liquid-phase bridging at the fiber cross nodes, which is beneficial to enhancing the structural integrity of the heat insulation pad under the scouring of high-temperature airflow; at the same time, the high refractive index nano metal oxide particles pre-composite to the surface of the glass powder together with the glass bridging phase constitute a local infrared extinction region, which is beneficial to suppressing heat transfer mainly by radiation during the high-temperature stage to a certain extent.

[0084] The inorganic fiber skeleton of the present invention adopts a dual-scale composite structure of chopped fibers and alumina fibers. The introduction of fine-diameter fibers helps to reduce the equivalent pore size of the fiber network, thereby suppressing the natural convection of the gas phase and gas phase heat transfer inside the pores, and reducing the equivalent thermal conductivity of the insulation pad in the medium and low temperature range. Detailed Implementation

[0085] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0086] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0087] The boron nitride nanosheets used in this application have a transverse particle size of 0.2-1 μm and a thickness of 30-100 nm; the nano-titanium dioxide has a particle size of 20-80 nm; the mullite chopped fibers have an average diameter of 3-7 μm; and the aramid precipitated fibers have an average fiber length of 0.1-2 mm and an average fiber diameter of 0.1-5 μm.

[0088] Example 1

[0089] This embodiment provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The preparation method specifically includes the following steps:

[0090] S1: Hydrated basic magnesium carbonate powder with a D50 of 15 μm and boron nitride nanosheets were dispersed in a mixed solvent at a mass ratio of 12:1. The volume ratio of deionized water to ethanol in the mixed solvent was 4:96, and the total mass of the hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of the mixed solvent was 1 g:8 mL. Silane coupling agent KH-560 was added, with the amount of coupling agent added being 2.5% of the total mass of the hydrated basic magnesium carbonate and boron nitride. The mixture was mechanically stirred at 55 °C for 3.5 h, followed by stirring at 58 °C and a pressure of -0.095. The concentrated slurry was obtained by rotary evaporation under reduced pressure at MPa until the slurry volume was reduced to 1 / 4 of the original volume. The concentrated slurry was then immersed in a cationic polydiallyldimethylammonium chloride aqueous solution with a concentration of 2.5 mg / mL for 35 min. The total mass ratio of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of cationic polydiallyldimethylammonium chloride aqueous solution was 1 g:18 mL. The slurry was then filtered and washed with deionized water until the conductivity of the filtrate was lower than 50 μS / cm. After vacuum drying at 75 °C for 7 h, the slurry was obtained as a stepped endothermic particle.

[0091] S2: Zinc oxide, boron oxide, silicon dioxide, and aluminum oxide were mixed in a mass ratio of 42:30:20:4 and placed in a crucible. The mixture was then heated to 1300℃ in a muffle furnace at a rate of 8℃ / min and held for 1.8h to melt. The melt was then quickly poured into deionized water for quenching to obtain glass fragments. After drying the glass fragments, they were wet-milled in a planetary ball mill with anhydrous ethanol as the grinding medium, a ball-to-material mass ratio of 4.5:1, and a rotation speed of 450rpm for 3.5h. The powder was then dried and sieved to obtain zinc borosilicate glass powder with a D50 of 12μm. This powder was then mixed with nano-titanium dioxide in a mass ratio of 18:1 and fed into a planetary ball mill without grinding balls. The mixture was ball-milled at a rotation speed of 2500rpm for 25min. After sieving, a bridged composite micro powder with a D50 of 18μm was obtained.

[0092] S3: Add deionized water to a pulper, add mullite chopped fibers and shear and pulp at 1800 rpm for 4 min; add alumina fibers with a diameter of 2 μm, continue dispersing at 1100 rpm for 2.5 min, add colloidal silica dropwise, stir at 700 rpm for 4 min, add stepped endothermic particles and stir for 8 min, add bridged composite micro powder and stir for 4 min, add aramid precipitated fibers, then adjust the pH to 8.5 using 0.8 mol / L sodium hydroxide solution, and add 0.08 wt.% of [unspecified ingredient]. A cationic polyacrylamide solution was stirred for 4 minutes to obtain a wet papermaking slurry with a solid content of 0.4 wt.%. Based on 100% of the total dry solids of the wet papermaking slurry: colloidal silica (based on SiO2 dry solids) 3.5 wt%, stepped endothermic particles 7 wt%, bridged composite micropowder 5 wt%, aramid precipitated fibers 1.2 wt%, and the balance being an inorganic fiber skeleton composed of mullite chopped fibers and alumina fibers in a mass ratio of 85:15. The cationic polyacrylamide solution accounted for 0.04% of the total dry solids of the wet papermaking slurry.

[0093] S4: The wet-processed pulp is poured into a fourdrinier paper machine and dewatered under negative pressure at a pressure of -0.05MPa for 2.5 minutes to obtain wet fiber felt. The wet felt is then transferred to a hot press dryer for staged drying: in the first stage, the temperature is increased at 1℃ / min and held at 95℃ for 50 minutes without external pressure; in the second stage, a second pressure of 0.04MPa is applied and the temperature is increased at 2℃ / min to 135℃ and held for 100 minutes; in the third stage, the temperature is increased at 1℃ / min and held for 50 minutes while maintaining the second pressure; after the process is completed, the pressure is released and the material is allowed to cool naturally in the furnace to obtain a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection.

[0094] Example 2

[0095] This embodiment provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The preparation method specifically includes the following steps:

[0096] S1: Hydrated basic magnesium carbonate powder with a D50 of 5 μm and boron nitride nanosheets were dispersed in a mixed solvent at a mass ratio of 5:1. The volume ratio of deionized water to ethanol in the mixed solvent was 2:98, and the total mass ratio of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of the mixed solvent was 1 g:5 mL. Silane coupling agent KH-560 was added, with the amount of coupling agent added being 1% of the total mass of hydrated basic magnesium carbonate and boron nitride. The mixture was mechanically stirred at 40 °C for 2 h, followed by stirring at 50 °C and a pressure of -0.08 MPa. A. Under reduced pressure, rotary evaporation was carried out until the slurry volume was reduced to 1 / 5 of the original volume to obtain a concentrated slurry. This concentrated slurry was then immersed in a cationic polydiallyldimethylammonium chloride aqueous solution with a concentration of 1 mg / mL for 20 min. The total mass ratio of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of cationic polydiallyldimethylammonium chloride aqueous solution was 1 g:10 mL. Subsequently, the slurry was filtered and washed with deionized water until the conductivity of the filtrate was lower than 50 μS / cm. The filtrate was then vacuum dried at 60 °C for 4 h to obtain stepped endothermic particles.

[0097] S2: Zinc oxide, boron oxide, silicon dioxide, and aluminum oxide were mixed in a mass ratio of 35:25:15:2 and placed in a crucible. The mixture was then placed in a muffle furnace and heated to 1150℃ at a rate of 5℃ / min and held for 1 hour to melt. The melt was then quickly poured into deionized water for quenching to obtain glass fragments. After drying the glass fragments, they were wet-milled in a planetary ball mill with anhydrous ethanol as the grinding medium, a ball-to-material mass ratio of 3:1, and a rotation speed of 300 rpm for 2 hours. The powder was then dried and sieved to obtain zinc borosilicate glass powder with a D50 of 5 μm. This powder was then mixed with nano-titanium dioxide in a mass ratio of 10:1 and fed into a planetary ball mill without grinding balls. The mixture was ball-milled at a rotation speed of 1500 rpm for 15 minutes and then sieved to obtain bridged composite micro powder with a D50 of 10 μm.

[0098] S3: Add deionized water to a pulper, add mullite chopped fibers and shear and pulp at 1000 rpm for 2 min; add alumina fibers with a diameter of 0.3 μm, continue dispersing at 800 rpm for 1 min, add colloidal silica dropwise, stir at 500 rpm for 3 min, add stepped endothermic particles and stir for 5 min, add bridged composite micro powder and stir for 3 min, add aramid precipitated fibers, then adjust the pH to 7.5 with 1 mol / L sodium hydroxide solution, and add 0.05 wt.% cation exchange resin. An ionic polyacrylamide solution was stirred for 2 minutes to obtain a wet papermaking slurry with a solid content of 0.1 wt.%. Based on 100% of the total dry solids of the wet papermaking slurry: colloidal silica (based on SiO2 dry solids) 1.5 wt%, stepped endothermic particles 4 wt%, bridging composite micropowder 2 wt%, aramid precipitated fibers 0.2 wt%, and the balance being an inorganic fiber skeleton composed of mullite chopped fibers and alumina fibers in a mass ratio of 75:25. The cationic polyacrylamide solution accounted for 0.01% of the total dry solids of the wet papermaking slurry.

[0099] S4: The wet-processed pulp is poured into a fourdrinier paper machine and dewatered under negative pressure at a pressure of -0.03 MPa for 1 minute to obtain wet fiber felt. The wet felt is then transferred to a hot press dryer for staged drying: in the first stage, the temperature is increased at 3℃ / min and held at 80℃ for 30 minutes without external pressure; in the second stage, a second pressure of 0.02 MPa is applied and the temperature is increased to 120℃ at a rate of 1℃ / min and held for 60 minutes; in the third stage, the temperature is increased to 150℃ at a rate of 1.3℃ / min and held for 30 minutes while maintaining the second pressure; after the process is completed, the pressure is released and the material is allowed to cool naturally in the furnace to obtain a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection.

[0100] Example 3

[0101] This embodiment provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The preparation method specifically includes the following steps:

[0102] S1: Hydrated basic magnesium carbonate powder with a D50 of 10 μm and boron nitride nanosheets were dispersed in a mixed solvent at a mass ratio of 8:1. The volume ratio of deionized water to ethanol in the mixed solvent was 3:97, and the total mass of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of the mixed solvent was 1 g:6 mL. Silane coupling agent KH-560 was added, with the amount of coupling agent added being 1.5% of the total mass of hydrated basic magnesium carbonate and boron nitride. The mixture was mechanically stirred at 45 °C for 2.5 h, and then at 52 °C and a pressure of -0.085 M. The concentrated slurry was obtained by rotary evaporation under reduced pressure until the volume of the slurry was reduced to 1 / 3.5 of the original volume. The slurry was then immersed in a cationic polydiallyldimethylammonium chloride aqueous solution with a concentration of 1.5 mg / mL for 25 min. The total mass ratio of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of cationic polydiallyldimethylammonium chloride aqueous solution was 1 g:12 mL. The slurry was then filtered and washed with deionized water until the conductivity of the filtrate was lower than 50 μS / cm. The filtrate was then vacuum dried at 65 °C for 5 h to obtain stepped endothermic particles.

[0103] S2: Zinc oxide, boron oxide, silicon dioxide, and aluminum oxide were mixed in a mass ratio of 40:32:18:5 and placed in a crucible. The mixture was then heated to 1200℃ in a muffle furnace at a rate of 7℃ / min and held for 1.2 hours to melt. The melt was then quickly poured into deionized water for quenching to obtain glass fragments. After drying the glass fragments, they were wet-milled in a planetary ball mill with anhydrous ethanol as the grinding medium, a ball-to-material mass ratio of 4:1, and a rotation speed of 350 rpm for 2.5 hours. The powder was then dried and sieved to obtain zinc borosilicate glass powder with a D50 of 10 μm. This powder was then mixed with nano-titanium dioxide in a mass ratio of 12:1 and fed into a planetary ball mill without grinding balls. The mixture was ball-milled at a rotation speed of 2000 rpm for 20 minutes. After sieving, a bridged composite micro powder with a D50 of 15 μm was obtained.

[0104] S3: Add deionized water to a pulper, add mullite chopped fibers and shear and pulp at 1200 rpm for 3 min; add alumina fibers with a diameter of 1 μm and continue to disperse at 900 rpm for 1.5 min; add colloidal silica dropwise and stir at 600 rpm for 4.5 min; add stepped endothermic particles and stir for 6 min; add bridged composite micro powder and stir for 4.5 min; add aramid precipitated fibers; then adjust the pH to 8.0 with 0.6 mol / L sodium hydroxide solution at a concentration of 0.1 wt. A cationic polyacrylamide solution was stirred for 3 minutes to obtain a wet papermaking slurry with a solid content of 0.2 wt.%. Based on 100% of the total dry solids of the wet papermaking slurry: colloidal silica (based on SiO2 dry solids) 2.0 wt%, stepped endothermic particles 5 wt%, bridged composite micropowder 3 wt%, aramid precipitated fibers 0.5 wt%, and the balance being an inorganic fiber skeleton composed of mullite chopped fibers and alumina fibers in a mass ratio of 95:5. The cationic polyacrylamide solution accounted for 0.02% of the total dry solids of the wet papermaking slurry.

[0105] S4: The wet-processed pulp is poured into a fourdrinier paper machine and dewatered under negative pressure at a pressure of -0.04 MPa for 1.5 min to obtain wet fiber felt. The wet felt is then transferred to a hot press dryer for staged drying: in the first stage, the temperature is increased at 2℃ / min and held at 85℃ for 40 min without external pressure; in the second stage, a second pressure of 0.03 MPa is applied and the temperature is increased at 0.5℃ / min to 125℃ and held for 80 min; in the third stage, the temperature is increased at 1.8℃ / min and held for 40 min while maintaining the second pressure; after the process is completed, the pressure is released and the material is allowed to cool naturally in the furnace to obtain a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection.

[0106] Example 4

[0107] This embodiment provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The preparation method specifically includes the following steps:

[0108] S1: Hydrated basic magnesium carbonate powder with a D50 of 20 μm and boron nitride nanosheets were dispersed in a mixed solvent at a mass ratio of 15:1. The volume ratio of deionized water to ethanol in the mixed solvent was 5:95, and the total mass ratio of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of the mixed solvent was 1 g:10 mL. Silane coupling agent KH-560 was added, with the amount of coupling agent added being 3% of the total mass of hydrated basic magnesium carbonate and boron nitride. The mixture was mechanically stirred at 60 °C for 4 h, followed by stirring at 60 °C and a pressure of -0.1 M. Reduced pressure rotary evaporation under pressure was carried out until the slurry volume was reduced to 1 / 3 of the original volume to obtain a concentrated slurry. This concentrated slurry was then immersed in a cationic polydiallyldimethylammonium chloride aqueous solution with a concentration of 3 mg / mL for 40 min. The total mass ratio of hydrated basic magnesium carbonate powder and boron nitride nanosheets to the volume ratio of cationic polydiallyldimethylammonium chloride aqueous solution was 1 g: 20 mL. Subsequently, the slurry was filtered and washed with deionized water until the conductivity of the filtrate was lower than 50 μS / cm. It was then vacuum dried at 80 °C for 8 h to obtain stepped endothermic particles.

[0109] S2: Zinc oxide, boron oxide, silicon dioxide, and aluminum oxide were mixed in a mass ratio of 45:35:25:6 and placed in a crucible. The mixture was then placed in a muffle furnace and heated to 1350℃ at a rate of 10℃ / min and held for 2 hours to melt. The melt was then quickly poured into deionized water for quenching to obtain glass fragments. After drying the glass fragments, they were wet-milled in a planetary ball mill with anhydrous ethanol as the grinding medium, a ball-to-material mass ratio of 5:1, and a speed of 500 rpm for 4 hours. The powder was then dried and sieved to obtain zinc borosilicate glass powder with a D50 of 15 μm. This powder was then mixed with nano-titanium dioxide in a mass ratio of 20:1 and fed into a planetary ball mill without grinding balls. The mixture was ball-milled at a speed of 3000 rpm for 30 minutes. After sieving, a bridged composite micro powder with a D50 of 20 μm was obtained.

[0110] S3: Add deionized water to a pulper, add mullite chopped fibers and shear and pulp at 2000 rpm for 5 min; add alumina fibers with a diameter of 3 μm and continue to disperse at 1200 rpm for 3 min; add colloidal silica dropwise, stir at 800 rpm for 5 min, then add stepped endothermic particles and stir for 10 min; add bridged composite micro powder and stir for 5 min; add aramid precipitated fibers, then adjust the pH to 9.0 using 0.5 mol / L sodium hydroxide solution, and add 0.085 wt.% of the solution. A cationic polyacrylamide solution was stirred for 5 minutes to obtain a wet papermaking slurry with a solid content of 0.5 wt.%. Based on 100% of the total dry solids of the wet papermaking slurry: colloidal silica (based on SiO2 dry solids) 4 wt%, stepped endothermic particles 8 wt%, bridged composite micropowder 6 wt%, aramid precipitated fibers 1.5 wt%, and the balance being an inorganic fiber skeleton composed of mullite chopped fibers and alumina fibers in a mass ratio of 80:20. The cationic polyacrylamide solution accounted for 0.05% of the total dry solids of the wet papermaking slurry.

[0111] S4: The wet-processed pulp is poured into a fourdrinier paper machine and dewatered under negative pressure at a pressure of -0.06 MPa for 3 minutes to obtain wet fiber felt. The wet felt is then transferred to a hot press dryer for staged drying: in the first stage, the temperature is increased at 2.5℃ / min and held at 100℃ for 60 minutes without external pressure; in the second stage, a second pressure of 0.05 MPa is applied and the temperature is increased to 140℃ at a rate of 1.5℃ / min and held for 120 minutes; in the third stage, the temperature is increased to 180℃ at a rate of 0.5℃ / min while maintaining the second pressure and held for 60 minutes. After the process is completed, the pressure is released and the material is allowed to cool naturally in the furnace to obtain a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection.

[0112] Comparative Example 1

[0113] This comparative example provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The difference from Example 1 is that step S1 is omitted and mullite short-cut fibers are used to replace the stepped heat-absorbing particles. Other operation steps and process parameters are exactly the same as in Example 1.

[0114] Comparative Example 2

[0115] This comparative example provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The difference from Example 1 is that step S2 is omitted, and mullite short-cut fibers are used to replace the bridging composite micro powder. Other operation steps and process parameters are exactly the same as in Example 1.

[0116] Comparative Example 3

[0117] This comparative example provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The difference from Example 1 is that boron nitride nanosheets are not added in step S1, while other operation steps and process parameters are exactly the same as in Example 1.

[0118] Comparative Example 4

[0119] This comparative example provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The difference from Example 1 is that after obtaining zinc borosilicate glass powder in S2, the dry mechanical composite treatment of nano titanium dioxide is not performed. The glass powder is directly used as bridging micro powder. Other operation steps and process parameters are exactly the same as in Example 1.

[0120] Comparative Example 5

[0121] This comparative example provides a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection and its preparation method. The difference from Example 1 is that aluminum hydroxide powder is used instead of hydrated basic magnesium carbonate powder in S1. Other operation steps and process parameters are exactly the same as in Example 1.

[0122] The performance of the ceramic nanofiber thermal insulation pads for lithium battery thermal runaway protection in Examples 1-4 and Comparative Examples 1-5 was tested, and the specific process is as follows:

[0123] Room temperature thermal conductivity test: The equivalent thermal conductivity of each sample in the thickness direction was measured at 25℃ using a heat flow method steady-state thermal conductivity meter in accordance with GB / T 10294 standard.

[0124] High-temperature thermal conductivity test: The equivalent thermal conductivity of each sample in the thickness direction was measured at 600℃ and 800℃ using a heat flow method steady-state thermal conductivity meter.

[0125] Thermal insulation performance test: A simulated thermal runaway test was conducted using a butane torch. The sample was horizontally fixed on the test stand, and the center of the hot surface of the sample was vertically ignited with a butane torch at a flame of 1300±50℃. A type K thermocouple was attached to the center of the cold surface of the sample, and the temperature change curve of the cold surface over time was continuously recorded. The test lasted for 600 seconds. The time required for the cold surface temperature to reach 200℃ (t) was recorded. 200 ( ) is used as an evaluation index for thermal insulation performance.

[0126] High-temperature structural integrity test: The sample is placed in a muffle furnace and heated to 800℃ at 10℃ / min and held for 30 min. Then it is cooled with the furnace. The mass retention rate of the sample before and after heat treatment is measured, and the appearance integrity of the sample is visually observed and recorded (whether there are cracks, powdering, scattering, etc.).

[0127] The test results are shown in Table 1.

[0128] Table 1. Performance test results of ceramic nanofiber thermal insulation pads for lithium battery thermal runaway protection in Examples 1-4 and Comparative Examples 1-5.

[0129]

[0130] From the test results of Example 1 and Comparative Example 1 in Table 1, it can be seen that the heat insulation pad, lacking the stepped heat-absorbing particles and the multi-stage decomposition heat absorption effect of the inorganic heat-absorbing core in the 220-550℃ temperature range, cannot continuously consume heat through thermochemical reactions when subjected to thermal shock. Therefore, the cold surface temperature rise rate is significantly accelerated in the butane torch test. 200 Shortened. Regarding steady-state thermal conductivity at room temperature and high temperature, since the replaced mullite fiber is made of the same material as the fiber skeleton in Example 1, the overall pore structure and thermal conductivity of the insulation pad have not fundamentally changed, so the difference in thermal conductivity at room temperature is small; however, in the steady-state tests at 600℃ and 800℃, due to the lack of the continuous heat absorption buffering effect and local heat diffusion assistance provided by the stepped heat-absorbing particles, heat is more easily transferred to the cold surface at high temperatures, resulting in an increase in high-temperature thermal conductivity. Regarding structural integrity at high temperatures, since it does not contain decomposable heat-absorbing components, the mass loss at high temperatures only comes from a small amount of degradation of the aramid precipitated fibers and the dehydroxylation condensation and water loss of colloidal silica, thus increasing the mass retention rate.

[0131] From the test results of Example 1 and Comparative Example 2 in Table 1, it can be seen that without the bridging composite micropowder, the structural reinforcement effect of low-melting-point glass softening and wetting the fiber cross nodes to form liquid-phase bridging is lacking. At 800℃, the fiber skeleton relies solely on the inorganic bonding provided by colloidal silica to maintain its connection. The inter-fiber bonding force is insufficient to resist the erosion of high-temperature airflow and thermal stress, resulting in obvious cracks and fiber pulverization and detachment in the samples, leading to a decrease in quality retention. Simultaneously, due to the lack of pre-embedded nano-titanium dioxide particles on the glass powder surface, the heat insulation pad's ability to scatter and absorb mid- and far-infrared thermal radiation is insufficient at high temperatures, increasing the radiative heat transfer component. Therefore, the steady-state thermal conductivity at 600℃ and 800℃ both increase. In the butane torch test, the combined degradation of structural damage and enhanced radiative heat transfer at high temperatures leads to a significantly accelerated rate of temperature rise on the cold surface. 200 Shortened. Regarding room temperature thermal conductivity, since the bridging composite micropowder does not participate in the construction of thermal conduction pathways at room temperature, its absence has a limited impact on the pore structure and gas phase thermal conductivity of the thermal insulation pad at room temperature. Therefore, the room temperature thermal conductivity is not significantly different from that of Example 1.

[0132] As shown in Table 1, the test results of Example 1 and Comparative Example 3 indicate that without the addition of boron nitride nanosheets, the multi-stage decomposition endothermic function of the heat-absorbing core itself is unaffected, resulting in minimal difference in steady-state thermal conductivity compared to Example 1. However, in the butane torch test, due to the lack of in-plane heat diffusion at the local micro-area level caused by the absence of boron nitride nanosheets, the localized high-temperature heat zone formed by the flame is more easily concentrated and transferred along the thickness direction, thus t 200 Shortened. Regarding high-temperature structural integrity, boron nitride nanosheets do not participate in the high-temperature liquid-phase bridging or structural reinforcement process, and their absence has no significant impact on the high-temperature connection state of the fiber skeleton. Therefore, the mass retention rate is basically the same as in Example 1. Regarding room-temperature thermal conductivity, since the volume content of boron nitride in the insulation pad is low and it is dispersed on the particle surface in a discontinuous semi-encapsulated form, its contribution to macroscopic steady-state thermal conductivity is limited. Therefore, the room-temperature thermal conductivity is not significantly different from that in Example 1.

[0133] From the test results of Example 1 and Comparative Example 4 in Table 1, it can be seen that the bridging micropowder of Comparative Example 4 contains glass powder but its surface is not composited with nano-titanium dioxide. The glass powder can still soften normally at high temperatures and form liquid-phase bridging at the fiber cross nodes. Therefore, the quality retention rate is close to that of Example 1, and the sample has good appearance integrity. However, due to the lack of distribution of high-refractive-index nano-titanium dioxide particles at the fiber nodes, the heat insulation pad's ability to scatter and absorb mid- and far-infrared thermal radiation is insufficient in the temperature range above 600°C. Radiative heat transfer becomes the main pathway for heat transfer in the high-temperature stage and is not effectively suppressed. Therefore, the steady-state thermal conductivity at 600°C and 800°C both increase. In the butane torch test, the increase in radiative heat transfer in the high-temperature stage accelerates the rate of temperature rise of the cold surface. 200 Shortened. Regarding room temperature thermal conductivity, nano-titanium dioxide does not constitute the main thermal conduction pathway in the insulation pad at room temperature, and its absence has no significant impact on the room temperature pore structure and gas phase thermal conductivity. Therefore, the room temperature thermal conductivity is basically the same as that in Example 1.

[0134] As shown in Table 1, the test results of Example 1 and Comparative Example 5 indicate that when aluminum hydroxide is used instead of hydrated basic magnesium carbonate as the endothermic core, both materials transform into alumina and magnesium oxide respectively at high temperatures. Their thermophysical properties are similar, and the framework structure and the composition of the bridging composite micropowder remain unchanged. Therefore, the steady-state thermal conductivity at room temperature and high temperature is similar to that of Example 1, and the high-temperature structural integrity also remains at a similar level. However, in the butane torch test, the thermal decomposition of aluminum hydroxide mainly occurred within a narrow temperature range of 200-350℃. Above 350℃, the endothermic reaction was essentially complete, and the endothermic capacity was rapidly depleted. At this point, the temperature continued to rise rapidly during thermal runaway, and the insulation pad lacked a continuous heat absorption and consumption mechanism within the 350-550℃ range. In contrast, the hydrated basic magnesium carbonate in Example 1 exhibits multi-stage decomposition characteristics, with its endothermic process extending to approximately 550℃. Within the 350-550℃ range, it can still continuously consume heat through carbonate decomposition reactions. Therefore, in the butane torch test, the cold surface temperature of Comparative Example 5 rose at a significantly faster rate in the medium-high temperature range than that of Example 1. 200 shorten.

[0135] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection, characterized in that, It contains at least the following components by total dry solids percentage: 4-8 wt.% of stepped heat-absorbing particles, wherein the stepped heat-absorbing particles comprise an inorganic heat-absorbing core and boron nitride nanosheets attached to the surface of the inorganic heat-absorbing core; 2-6 wt% of bridging composite micro powder, wherein the bridging composite micro powder comprises glass powder and nano-metal oxide particles composited on the surface of the glass powder; The remainder is an inorganic fiber skeleton.

2. The ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 1, characterized in that, The inorganic endothermic core is hydrated basic magnesium carbonate, and the mass ratio of the inorganic endothermic core to the boron nitride nanosheets is (5-15):1; the outer surface of the stepped endothermic particles has a cationic polymer modified layer.

3. The ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 1, characterized in that, The glass powder is zinc borosilicate glass powder, which comprises zinc oxide, boron oxide, silicon dioxide and aluminum oxide, with a mass ratio of (35-45):(25-35):(15-25):(2-6); the nano-metal oxide particles are nano-titanium dioxide, with a mass ratio of glass powder to nano-metal oxide particles of (10-20):

1.

4. The ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 1, characterized in that, The inorganic fiber skeleton comprises mullite chopped fibers and alumina fibers with a diameter of 0.3-3 μm, wherein the mass ratio of the mullite chopped fibers to the alumina fibers is (75-95):(25-5).

5. A ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 1, characterized in that, The thermal insulation pad also contains 1.5-4 wt% colloidal silica and 0.2-1.5 wt% aramid precipitated fibers, based on the total dry solids percentage.

6. A method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: Inorganic endothermic core powder and boron nitride nanosheets were dispersed in a mixed solvent containing a silane coupling agent and stirred. After being concentrated by vacuum evaporation, they were surface modified in a cationic polymer aqueous solution, washed and dried to obtain stepped endothermic particles. Glass raw materials are mixed and then melted at high temperature, quenched in water, and crushed to obtain glass powder. The glass powder is then subjected to dry mechanical composite treatment with nano-metal oxide particles to obtain bridging composite micro powder. After dispersing the inorganic fiber skeleton in water, colloidal silica is added to adsorb onto the fiber surface. Then, the stepped heat-absorbing particles and the bridging composite micro powder are added sequentially for dispersion and mixing. Aramid precipitated fibers are added, and cationic flocculants are added after adjusting the pH to obtain wet papermaking slurry. The wet papermaking slurry is dehydrated and molded under negative pressure to obtain wet fiber felt, which is then subjected to segmented heating and drying to obtain a ceramic nanofiber heat insulation pad for lithium battery thermal runaway protection.

7. The method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 6, characterized in that, In the step of preparing the stepped endothermic particles, the reduced pressure evaporation is carried out at 50-60℃ and a pressure of -0.08~-0.1MPa until the slurry volume is reduced to 1 / 5-1 / 3 of the original volume; the cationic polymer is polydiallyldimethylammonium chloride, and its aqueous solution concentration is 1-3mg / mL, and the treatment time is 20-40min; the filtrate is washed until the conductivity is lower than 50μS / cm, and then vacuum dried at 60-80℃ for 4-8h.

8. The method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 6, characterized in that, In the step of preparing the bridged composite micro powder, the glass raw materials include zinc oxide, boron oxide, silicon dioxide and aluminum oxide; the high-temperature melting conditions are to heat to 1150-1350℃ at a rate of 5-10℃ / min and hold at that temperature for 1-2 hours.

9. A method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 6, characterized in that, In the steps of preparing bridged composite micro powder, the crushing is carried out in a planetary ball mill with anhydrous ethanol as the wet grinding medium, a ball-to-material mass ratio of (3-5):1, and a rotation speed of 300-500 rpm for 2-4 hours, followed by drying and sieving; the dry mechanical composite treatment is carried out in a planetary ball mill without grinding balls at a rotation speed of 1500-3000 rpm for 15-30 minutes.

10. The method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 6, characterized in that, In the preparation steps of wet papermaking slurry, the solid content of the wet papermaking slurry is 0.1-0.5 wt%, and the pH is adjusted to 7.5-9.0 using a 0.5-1 mol / L sodium hydroxide solution; the cationic flocculant is a cationic polyacrylamide solution, and its addition amount is 0.01-0.05% of the total dry solids mass of the slurry.

11. A method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 6, characterized in that, The negative pressure filtration pressure is -0.03 to -0.06 MPa, and the dehydration time is 1-3 minutes.

12. The method for preparing a ceramic nanofiber thermal insulation pad for lithium battery thermal runaway protection according to claim 6, characterized in that, The segmented heating and drying process includes: a first stage of holding at 80-100℃ for 30-60 minutes without external pressure; a second stage of applying pressure of 0.02-0.05MPa and heating to 120-140℃ and holding for 60-120 minutes; and a third stage of heating to 150-180℃ and holding for 30-60 minutes while maintaining the pressure.

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