Ceramic diaphragm as well as preparation method and application thereof

Abstract

The invention relates to the technical field of battery diaphragms, in particular to a ceramic diaphragm as well as a preparation method and application thereof. The material of the ceramic diaphragm provided by the invention comprises amino silicon dioxide, low-molecular-weight meta-aramid and high-molecular-weight meta-aramid. The meta-position aramid fiber with low molecular weight is coated on the surface of the amino silicon dioxide through a cross-linking agent; the meta-position aramid fiber with high molecular weight and the meta-position aramid fiber with low molecular weight are connected in a molecular winding manner; the viscosity average molecular weight of the meta-position aramid fiber with the low molecular weight is 1 to 7W; the viscosity average molecular weight of the meta-position aramid fiber with the high molecular weight is 10 to 20W. The ceramic diaphragm can obviously improve the cycling stability of the secondary lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery diaphragms, and in particular to a ceramic diaphragm and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, due to their advantages such as high operating voltage, high energy density, and long cycle life, are playing an increasingly important role in electronic products and electric vehicles. However, with the increasing application of lithium-ion batteries, the separator, as a barrier between the positive and negative electrodes, also plays a vital role in the performance of lithium-ion batteries.

[0003] Currently, most commercial lithium-ion battery separators are typically made of polyolefin materials. However, these materials often have poor liquid absorption, thermal stability, and mechanical strength, seriously affecting battery safety. To address these issues, the prior art typically applies a coating to the surface of the polyolefin separator. While inorganic coatings can effectively improve the separator's high-temperature resistance, they have poor bonding with the base film, making them prone to powder loss. This, in turn, leads to poor separator penetration and resistance to lithium dendrites, ultimately affecting the cycling stability of the lithium-ion battery. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a ceramic diaphragm and its preparation method and application. The ceramic diaphragm can significantly improve the cycle stability of secondary lithium batteries.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a ceramic diaphragm, wherein the material of the ceramic diaphragm includes aminosilica, low molecular weight meta-aramid and high molecular weight meta-aramid;

[0007] The low molecular weight meta-aramid is coated on the surface of the aminosilica through a cross-linking agent;

[0008] The high molecular weight meta-aramid and the low molecular weight meta-aramid are connected in a molecular entanglement manner;

[0009] The viscosity average molecular weight of the low molecular weight meta-aramid is 1 to 7W;

[0010] The viscosity average molecular weight of the high molecular weight meta-aramid is 10-20W.

[0011] Preferably, the high molecular weight meta-aramid is not connected to aminosilica;

[0012] Or part of the high molecular weight meta-aramid fiber is connected to aminosilica via a crosslinking agent.

[0013] Preferably, the cross-linking agent is an isocyanate compound containing two or more isocyanate groups;

[0014] The isocyanate groups in the isocyanate compound are cross-linked with the amino groups in the aminosilica and the amino groups in the low molecular weight meta-aramid respectively;

[0015] Or the isocyanate group in the isocyanate compound is cross-linked with the amino group in the aminosilica, the amino group in the low molecular weight meta-aramid, or the amino group in the high molecular weight meta-aramid.

[0016] Preferably, the crosslinking agent includes one or more of p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthalene 1,5-diisocyanate, p-phenylene diisocyanate and triphenylmethane triisocyanate.

[0017] Preferably, the low molecular weight meta-aramid slurry for preparing the ceramic diaphragm has a solid content of 12 to 20 wt %, a rotational viscosity of 10,000 to 90,000 mP·s, and an inherent viscosity of 1.3 to 1.8 dl / g;

[0018] The high molecular weight meta-aramid slurry for preparing the ceramic diaphragm has a solid content of 12-20 wt%, a rotational viscosity of 200,000-2,000,000 mP·s, and an inherent viscosity of 2.3-3.2 dl / g.

[0019] Preferably, the method for preparing the low molecular weight meta-aramid slurry comprises the following steps:

[0020] Under protective atmosphere, stirring and circulating cooling conditions, the first m-phenylenediamine and isophthaloyl chloride are sequentially added to N,N-dimethylacetamide, the above process of adding the isophthaloyl chloride is repeated three times, the isophthaloyl chloride is added for the fifth time, and the second m-phenylenediamine is added for end-capping treatment to obtain the low molecular weight meta-aramid slurry;

[0021] The end-capping treatment is carried out under static conditions, and the time of the end-capping treatment is 5 to 8 hours.

[0022] Preferably, the method for preparing the high molecular weight meta-aramid slurry comprises the following steps:

[0023] Under the conditions of protective atmosphere, stirring and circulating cooling, the first m-phenylenediamine and isophthaloyl chloride are added to N,N-dimethylacetamide in sequence, and the above process of adding the isophthaloyl chloride is repeated three times. Then, isophthaloyl chloride is added for the fifth time, and the reaction is continued under circulating cooling, the circulating cooling is stopped and the reaction is continued, and the reaction is allowed to stand, thereby obtaining the high molecular weight m-aramid slurry.

[0024] The present invention also provides a method for preparing the ceramic diaphragm described in the above technical solution, comprising the following steps:

[0025] After mixing low molecular weight meta-aramid slurry and amino silica, a cross-linking agent is added to obtain a ceramic mixed slurry;

[0026] Mixing the ceramic mixed slurry and high molecular weight meta-aramid slurry to obtain a membrane-making slurry;

[0027] The membrane-forming slurry is formed into a membrane to obtain the ceramic separator.

[0028] Preferably, the mixing of the low molecular weight meta-aramid slurry and aminosilica is carried out in a protective atmosphere at a dew point of -40°C to -60°C;

[0029] The mixing is carried out under stirring conditions, the stirring speed is 100 to 500 rpm, and the time is 1 to 6 hours;

[0030] The mass ratio of the aminosilica to the low molecular weight meta-aramid slurry is (0.5-10):100.

[0031] Preferably, the mass ratio of the p-phenylene diisocyanate to the low molecular weight meta-aramid slurry is (0.1-5):100;

[0032] The mass ratio of the ceramic mixed slurry to the membrane-forming slurry is (0.5-10):100.

[0033] The present invention also provides the use of the ceramic diaphragm described in the above technical solution or the ceramic diaphragm prepared by the preparation method described in the above technical solution in a secondary lithium battery.

[0034] Preferably, the secondary lithium battery is a secondary lithium-free negative electrode battery.

[0035] The present invention provides a ceramic diaphragm, the materials of which include aminosilica, low molecular weight meta-aramid, and high molecular weight meta-aramid; the low molecular weight meta-aramid is coated on the surface of the aminosilica by a crosslinking agent; the high molecular weight meta-aramid and the low molecular weight meta-aramid are connected by molecular entanglement; the viscosity-average molecular weight of the low molecular weight meta-aramid is 1 to 7W; and the viscosity-average molecular weight of the high molecular weight meta-aramid is 10 to 20W. The aminosilica in the ceramic diaphragm of the present invention is crosslinked with the low molecular weight meta-aramid by a crosslinking agent to form an interactive coating composite material; the crosslinking agent crosslinks the aminosilica with the amino groups in the low molecular weight meta-aramid to form a coating layer. Furthermore, the low molecular weight meta-aramid has relatively more amino groups in its end groups, and the amino groups in the aminosilica form tighter crosslinks with the end groups of the low molecular weight meta-aramid. The addition of high molecular weight meta-aramid provides sufficient membrane strength for the diaphragm. Therefore, the ceramic diaphragm of the present invention has significant improvements in puncture performance and thermal shrinkage performance, thereby improving the cycle stability of the secondary lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the ceramic diaphragm of the present invention and the connection relationship between aminosilica and low molecular weight meta-aramid, wherein 1 is aminosilica, 2 is low molecular weight meta-aramid, and 3 is high molecular weight meta-aramid;

[0037] Figure 2 This is a SEM image of the ceramic diaphragm described in Example 1;

[0038] Figure 3 This is the cycle performance curve of the 2032-type button battery prepared with the ceramic diaphragm described in Example 1;

[0039] Figure 4 This is the cycle performance curve of the 2032-type button battery prepared using the ceramic diaphragm described in Comparative Example 1. DETAILED DESCRIPTION

[0040] like Figure 1 The present invention provides a ceramic diaphragm, wherein the material of the ceramic diaphragm includes amino silicon dioxide, low molecular weight meta-aramid and high molecular weight meta-aramid;

[0041] The low molecular weight meta-aramid is coated on the surface of the aminosilica through a cross-linking agent;

[0042] The high molecular weight meta-aramid and the low molecular weight meta-aramid are connected in a molecular entanglement manner;

[0043] The viscosity average molecular weight of the low molecular weight meta-aramid is 1 to 7W;

[0044] The viscosity average molecular weight of the high molecular weight meta-aramid is 10-20W.

[0045] In the present invention, the high molecular weight meta-aramid is preferably not connected to aminosilica; or part of the high molecular weight meta-aramid is preferably connected to aminosilica via a crosslinking agent (such as Figure 1 (as shown in a in the figure).

[0046] In the present invention, the cross-linking agent is an isocyanate compound comprising two or more isocyanate groups; the isocyanate groups in the isocyanate compound are cross-linked with the amino groups in the aminosilica and the amino groups in the low molecular weight meta-aramid respectively; or the isocyanate groups in the isocyanate compound are cross-linked with the amino groups in the aminosilica, the amino groups in the low molecular weight meta-aramid or the amino groups in the high molecular weight meta-aramid respectively (such as Figure 1 As shown in b, the low molecular weight meta-aramid in b is an example of a case where the end group of the successfully capped fiber is an amino group).

[0047] In the present invention, the amino groups in the low molecular weight meta-aramid or the amino groups in the aminosilica are cross-linked with the isocyanate groups in the isocyanate compounds to generate urea groups (such as Figure 1 (as shown in c in the figure).

[0048] In the present invention, the crosslinking agent preferably includes one or more of p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, and triphenylmethane triisocyanate. When the crosslinking agent is two or more of the above-mentioned specific selections, the present invention does not have any special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the crosslinking agent is specifically p-phenylene diisocyanate.

[0049] In the present invention, the low molecular weight meta-aramid slurry for preparing the ceramic diaphragm preferably has a solid content of 12 to 20 wt %, a rotational viscosity of 10,000 to 90,000 mP·s, and an inherent viscosity of 1.3 to 1.8 dl / g;

[0050] The high molecular weight meta-aramid slurry for preparing the ceramic diaphragm preferably has a solid content of 12 to 20 wt %, a rotational viscosity of 200,000 to 2,000,000 mP·s, and an inherent viscosity of 2.3 to 3.2 dl / g.

[0051] In the present invention, the solid content of the low molecular weight meta-aramid slurry is preferably 12 to 20 wt%, more preferably 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%; the rotational viscosity is preferably 10,000 to 90,000 mP·s, more preferably 10,000 mP·s, 20,000 mP·s, 30,000 mP·s, 40,000 mP·s, 50,000 mP·s, 60,000 mP·s, 70,000 mP·s, 80,000 mP·s or 90,000 mP·s; the inherent logarithmic viscosity is preferably 1.3 to 1.8 dl / g, more preferably 1.3 dl / g, 1.4 dl / g, 1.5 dl / g, 1.6 dl / g, 1.7 dl / g or 1.8 dl / g. In an embodiment of the present invention, the low molecular weight meta-aramid slurry may have a solid content of 17 wt %, a rotational viscosity of 37122 mP·s or 83810 mP·s, an inherent viscosity of 1.58 dl / g or 1.8 dl / g, and a viscosity-average molecular weight of 23134.

[0052] In the present invention, the method for preparing the low molecular weight meta-aramid slurry preferably comprises the following steps:

[0053] Under protective atmosphere, stirring and circulating cooling conditions, the first m-phenylenediamine and isophthaloyl chloride are sequentially added to N,N-dimethylacetamide, the above process of adding the isophthaloyl chloride is repeated three times, the isophthaloyl chloride is added for the fifth time, and the second m-phenylenediamine is added for end-capping treatment to obtain the low molecular weight meta-aramid slurry;

[0054] The end-capping treatment is carried out under static conditions, and the time of the end-capping treatment is 5 to 8 hours.

[0055] The present invention does not have any particular limitation on the type of protective atmosphere, and any type familiar to those skilled in the art may be used. In an embodiment of the present invention, the protective atmosphere may be a nitrogen atmosphere. In the present invention, the temperature for adding m-phenylenediamine is preferably -10 to 0°C, more preferably -10°C, -9°C, -8°C, -7°C, -6°C, -5°C, -4°C, -3°C, -2°C, -1°C or 0°C. In an embodiment of the present invention, the temperature for adding m-phenylenediamine may be -5°C.

[0056] In the present invention, the temperature of adding m-phenylenediamine is preferably cooled by an external cooling circulation system at -30°C.

[0057] In the present invention, the process of adding the m-phenylenediamine is preferably carried out under stirring, and the process of continuing to stir after the addition of the m-phenylenediamine is completed is preferably carried out; the speed of the stirring and continuing stirring is preferably 50 to 150 rpm, more preferably 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm or 150 rpm; the present invention has no special restrictions on the process of adding the m-phenylenediamine, and can be carried out using a process well known to those skilled in the art. The present invention has no special restrictions on the time of continuing to stir, as long as it can ensure that the m-phenylenediamine is completely dissolved in the N,N-dimethylacetamide.

[0058] In the present invention, the mass ratio of the first m-phenylenediamine to the N,N-dimethylacetamide is preferably 200:2000.

[0059] In the present invention, the temperature for adding the isophthaloyl chloride is preferably -20 to 0° C., more preferably -20° C., -19° C., -18° C., -17° C., -16° C., -15° C., -14° C., -13° C., -12° C., -11° C., -10° C., -9° C., -8° C., -7° C., -6° C., -5° C., -4° C., -3° C., -2° C., -1° C. or 0° C. In an embodiment of the present invention, the temperature for adding the isophthaloyl chloride may be -15° C.

[0060] In the present invention, the mass ratio of the isophthaloyl chloride added in each of the first four times to the N,N-dimethylacetamide is preferably (50-80):2000, more preferably 50:2000, 60:2000, 70:2000 or 80:2000. In an embodiment of the present invention, the mass ratio of the isophthaloyl chloride added in each of the first four times to the N,N-dimethylacetamide can be 46.94:2000.

[0061] In the present invention, the mass of isophthaloyl chloride added each time for the first four times is preferably the same.

[0062] In the present invention, the molar amount of isophthaloyl chloride added for the fifth time is preferably the sum of the molar amounts of isophthaloyl chloride added for the first four times.

[0063] In the present invention, the total molar amount of the added isophthaloyl dichloride is preferably equal to the molar amount of the m-phenylenediamine.

[0064] In the present invention, the addition of the isophthaloyl chloride is preferably carried out under stirring, and the stirring speed is preferably 100 to 300 rpm, more preferably 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm, 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm or 300 rpm. In an embodiment of the present invention, the stirring speed can be 150 rpm.

[0065] In the present invention, the temperature for adding the isophthaloyl chloride for the fifth time is preferably -20°C to -10°C, more preferably -20°C, -19°C, -18°C, -17°C, -16°C, -15°C, -14°C, -13°C, -12°C, -11°C or -10°C. In an embodiment of the present invention, the temperature for adding the isophthaloyl chloride for the fifth time may be -15°C.

[0066] In the present invention, after the fifth addition of the isophthaloyl chloride is completed, the reaction is preferably continued for 0.5 to 3 hours, more preferably 0.5 hours, 0.8 hours, 1.2 hours, 1.5 hours, 1.8 hours, 2.2 hours, 2.5 hours, 2.8 hours or 3 hours. In an embodiment of the present invention, the reaction time can be 1.5 hours.

[0067] In the present invention, the percentage of the molar amount of the second meta-phenylenediamine to the molar amount of the first meta-phenylenediamine is preferably 0.5-3%, more preferably 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3%. In an embodiment of the present invention, the percentage of the molar amount of the second meta-phenylenediamine to the total molar amount of the first meta-phenylenediamine can be 1% or 0.5%.

[0068] In the present invention, the end-capping treatment is preferably carried out under standing conditions, and the standing time is preferably 5 to 8 hours, more preferably 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours. In an embodiment of the present invention, the standing time can be 8 hours.

[0069] In the present invention, the solid content of the high molecular weight meta-aramid slurry is preferably 12 to 20 wt%, more preferably 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%; the rotational viscosity is preferably 200,000 to 2,000,000 mP·s, more preferably 200,000 mP·s, 300,000 mP·s, 400,000 mP·s, 500,000 mP·s, 600,000 mP·s, 700,000 mP·s, 800,000 mP·s, 900,000 mP·s, 1,000,000 mP·s, 110 The inherent viscosity is preferably 2.3 to 3.2 dl / g, more preferably 2.3 dl / g, 2.4 dl / g, 2.5 dl / g, 2.6 dl / g, 2.7 dl / g, 2.8 dl / g, 2.9 dl / g, 3.0 dl / g, 3.1 dl / g or 3.2 dl / g. In an embodiment of the present invention, the high molecular weight meta-aramid slurry may have a solid content of 17 wt %, a rotational viscosity of 562354 mP·s or 1735642 mP·s, and an inherent viscosity of 2.38 dl / g or 3.05 dl / g.

[0070] In the present invention, the method for preparing the high molecular weight meta-aramid slurry preferably comprises the following steps:

[0071] Under the conditions of protective atmosphere, stirring and circulating cooling, the first m-phenylenediamine and isophthaloyl chloride are added to N,N-dimethylacetamide in sequence, and the above process of adding the isophthaloyl chloride is repeated three times. Then, isophthaloyl chloride is added for the fifth time, and the reaction is continued under circulating cooling, the circulating cooling is stopped and the reaction is continued, and the reaction is allowed to stand, thereby obtaining the high molecular weight m-aramid slurry.

[0072] In the present invention, the process of "adding a first m-phenylenediamine and isophthaloyl chloride in N,N-dimethylacetamide in sequence under the conditions of protective atmosphere, stirring and circulating cooling, repeating the above process of adding the isophthaloyl chloride three times, and then adding isophthaloyl chloride for the fifth time" is preferably referred to the method for preparing a low molecular weight meta-aramid slurry described in the above technical solution, and will not be repeated again.

[0073] In the present invention, the reaction is continued under circulating cooling conditions and is preferably carried out under stirring conditions. The stirring temperature is preferably -10 to -20°C, more preferably -10°C, -11°C, -12°C, 013°C, -14°C, -15°C, -16°C, -17°C, -18°C, -19°C or -20°C; the stirring speed is preferably 100 to 150 rpm, more preferably 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm or 150 rpm; the time is preferably 10 to 60 min, more preferably 10 min, 20 min, 30 min, 40 min, 50 min or 60 min. In an embodiment of the present invention, the temperature of the reaction continued under circulating cooling conditions can be -10°C, the speed can be 150 rpm, and the time can be 30 min.

[0074] In the present invention, stopping the circulation cooling and continuing the reaction is preferably carried out under stirring conditions, and the stirring temperature is preferably 15 to 30 ° C, more preferably 15 ° C, 16 ° C, 17 ° C, 18 ° C, 19 ° C, 20 ° C, 21 ° C, 22 ° C, 23 ° C, 24 ° C, 25 ° C, 26 ° C, 27 ° C, 28 ° C, 29 ° C or 30 ° C; the stirring speed is preferably 100 to 500 rpm, more preferably 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm; the time is preferably 2 to 5 h, more preferably 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h. In an embodiment of the present invention, the temperature of stopping the circulation cooling and continuing the reaction can be 15 to 30 ° C, the time can be 2 h, and the speed can be 300 rpm.

[0075] In the present invention, the standing temperature is preferably >15°C; and the standing time is preferably ≥6h.

[0076] The present invention also provides a method for preparing the ceramic diaphragm described in the above technical solution, comprising the following steps:

[0077] After mixing low molecular weight meta-aramid slurry and amino silica, a cross-linking agent is added to obtain a ceramic mixed slurry;

[0078] Mixing the ceramic mixed slurry and high molecular weight meta-aramid slurry to obtain a membrane-making slurry;

[0079] The membrane-forming slurry is formed into a membrane to obtain the ceramic separator.

[0080] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0081] The invention mixes low-molecular-weight meta-aramid slurry and aminosilica, and then adds a cross-linking agent to obtain a ceramic mixed slurry.

[0082] In the present invention, the preparation method of aminosilica preferably comprises the following steps:

[0083] In a 250mL three-necked flask, 19g of Triton X-100, 77mL of cyclohexane, 16mg of n-hexanol and 3.4mL of deionized water were added respectively, and stirred at 300rpm for 15min. Then, 25% ammonia water was added to make the pH of the solution 8, 1mL of ethyl orthosilicate was added, and stirred at 1500rpm for 2min, and then stirred at 400rpm for 1h. Then, 0.4mL of 3-(trihydroxysilyl)propylmethylphosphonate was added and stirred for 10min. Finally, 0.1mL of 3-(aminopropyl)triethoxysilane was added and stirred for 24h. The mixture was washed with ethanol 5 times and with pure water 3 times by suction filtration, and dried in a vacuum oven at 110°C to obtain the aminosilica for standby use.

[0084] In the present invention, the low molecular weight meta-aramid slurry and aminosilica are mixed in a protective atmosphere. The present invention does not have any particular limitation on the type of the protective atmosphere, and an inert atmosphere well known to those skilled in the art can be used. In an embodiment of the present invention, the protective atmosphere can be a nitrogen atmosphere.

[0085] In the present invention, the mixing temperature of the low molecular weight meta-aramid slurry and aminosilica is preferably -40°C to -60°C, more preferably -40°C, -45°C, -50°C, -55°C or -60°C. In an embodiment of the present invention, the mixing temperature of the low molecular weight meta-aramid slurry and aminosilica may be -40°C, dew point.

[0086] In the present invention, the mixing is preferably carried out under stirring conditions, the stirring speed is preferably 100-500 rpm, more preferably 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm; the time is preferably 1-6 hours, more preferably 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours. In an embodiment of the present invention, the stirring speed can be 100 rpm and the time can be 2 hours.

[0087] In the present invention, the mass ratio of the aminosilica to the solids in the low molecular weight meta-aramid slurry is preferably (0.5-10):100, more preferably 0.5:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, 5.5:100, 6:100, 6.5:100, 7:100, 7.5:100, 8:100, 8.5:100, 9:100, 9.5:100 or 10:100. In an embodiment of the present invention, the mass ratio of the aminosilica to the low molecular weight meta-aramid slurry may be 3:100 or 10:100.

[0088] The present invention does not have any special limitation on the process of adding the cross-linking agent, and the process well known to those skilled in the art can be used.

[0089] In the present invention, the mass ratio of the crosslinking agent to the solids in the low molecular weight meta-aramid slurry is preferably (0.1-5):100, more preferably 0.1:100, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100 or 5:100. In an embodiment of the present invention, the mass ratio of the crosslinking agent to the low molecular weight meta-aramid slurry may be 1:100 or 3:100.

[0090] After adding the crosslinking agent, the present invention further preferably includes a process of continuing the reaction. The continued reaction is preferably carried out under stirring, and the stirring speed is preferably the same as the stirring speed in the previous process. The continued reaction time is preferably 0.5 to 6 hours, more preferably 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours. In an embodiment of the present invention, the continued reaction time can be 0.5 hours.

[0091] After mixing the ceramic slurry, the present invention mixes the ceramic mixed slurry with a high molecular weight meta-aramid slurry to obtain a membrane-making slurry.

[0092] The present invention has no special limitation on the mixing of the ceramic mixed slurry and the high molecular weight meta-aramid slurry, and the mixing can be carried out using a process well known to those skilled in the art.

[0093] In the present invention, the mass ratio of the ceramic mixed slurry to the membrane slurry is preferably (0.5-10):100, more preferably 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100. In an embodiment of the present invention, the mass ratio of the ceramic mixed slurry to the membrane slurry can be 5:100 or 10:100.

[0094] After obtaining the membrane-forming slurry, the present invention forms a membrane from the membrane-forming slurry to obtain the ceramic diaphragm.

[0095] In the present invention, the film-forming method is preferably non-solvent phase separation film-forming; the non-solvent phase separation film-forming preferably includes die extrusion, gelation, stretching, water washing, drying and heat setting performed in sequence.

[0096] In the present invention, the extrusion temperature of the die is preferably 15-25°C, more preferably 20°C; the die shape of the die is preferably a hanger die; the extrusion pressure of the die is preferably 0-5MPa, more preferably 2MPa.

[0097] In the present invention, the non-solvent in the gel tank for gelation preferably includes water and / or alcohol; the solvent in the gel tank for gelation preferably includes one or more of DMAC, DMF, and NMP. When the non-solvent or solvent is two or more of the above-mentioned specific selections, the present invention does not have any special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In the present invention, the mass ratio of the non-solvent to the solvent is preferably (20-50):100, more preferably 20:100, 30:100, 40:100, or 50:100. In an embodiment of the present invention, the non-solvent can be water and the solvent can be DMAC; the mass ratio of the non-solvent to the solvent can be 3:7.

[0098] In the present invention, the gelation time is preferably 0.5 to 5 minutes, more preferably 0.5 minutes, 1 minute, 2 minutes, 3 minutes, 4 minutes or 5 minutes. In an embodiment of the present invention, the gelation time can be 1 minute.

[0099] In the present invention, the stretching is preferably biaxial stretching; the stretching ratio of the biaxial stretching is preferably 1.2 to 1.5, more preferably 1.2, 1.3, 1.4 or 1.5. In an embodiment of the present invention, the stretching ratio of the biaxial stretching can be 1.3 times.

[0100] In the present invention, the water washing temperature is preferably 20-70°C, more preferably 20°C, 30°C, 40°C, 50°C, 60°C or 70°C; the water washing time is preferably 3-10 minutes, more preferably 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes. In an embodiment of the present invention, the water washing temperature can be 50°C and the time can be 3 minutes.

[0101] In the present invention, the drying temperature is preferably 60-80°C, more preferably 60°C, 65°C, 70°C, 75°C or 80°C; the drying time is preferably 1-3 minutes, more preferably 1 minute, 2 minutes or 3 minutes. In an embodiment of the present invention, the drying temperature can be 80°C and the drying time can be 2 minutes.

[0102] In the present invention, the heat setting temperature is preferably 250-320°C, more preferably 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C or 320°C; the heat setting time is preferably 1-5 minutes, more preferably 1 minute, 2 minutes, 3 minutes, 4 minutes or 5 minutes. In an embodiment of the present invention, the heat setting temperature can be 270°C and the time can be 1 minute.

[0103] In the present invention, the preparation method uses a low molecular weight meta-aramid slurry to utilize the relatively more amino groups in its end groups. When the amino groups in the aminosilica and the end groups of the low molecular weight meta-aramid are cross-linked, a special coating pattern and chemical bond link are formed. This coating pattern significantly improves the puncture performance and thermal shrinkage performance of the diaphragm prepared after the high molecular weight meta-aramid slurry is incorporated, thereby improving the cycle stability of the secondary lithium battery.

[0104] The present invention also provides a ceramic diaphragm prepared by the preparation method described in the above technical solution. In the present invention, the thickness of the ceramic diaphragm is preferably 5 to 20 μm. In an embodiment of the present invention, the thickness of the ceramic diaphragm can be 10 μm or 15 μm.

[0105] The present invention also provides the use of the ceramic diaphragm described in the above technical solution in a secondary lithium battery.

[0106] In the present invention, the secondary lithium battery is preferably a secondary lithium-free negative electrode battery.

[0107] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0108] Example 1

[0109] Preparation of aminosilica: In a 250mL three-necked flask, 19g of TritonX-100, 77mL of cyclohexane, 16mg of n-hexanol and 3.4mL of deionized water were added respectively, and stirred at 300rpm for 15min, and then 25% ammonia water was added to make the pH of the solution = 8, 1mL of ethyl orthosilicate was added, and stirred at 1500rpm for 2min, and then stirred at 400rpm for 1h, and then 0.4mL of 3-(trihydroxysilyl)propylmethylphosphonate was added and stirred for 10min, and finally 0.1mL of 3-(aminopropyl)triethoxysilane was added and stirred for 24h, and then washed with ethanol 5 times and pure water 3 times by suction filtration, and dried in a vacuum oven at 110°C to obtain the aminosilica for standby use;

[0110] Preparation of low molecular weight meta-aramid slurry: 2000g of N,N-dimethylacetamide was added to the reactor, and nitrogen was introduced (the whole process was carried out in a nitrogen atmosphere), and an external cooling circulation system of -30°C was used for cooling. When the temperature dropped to -5°C, 200g of m-phenylenediamine was added, and the mixture was stirred at 150rpm for 60min until the m-phenylenediamine was completely dissolved. The temperature in the reactor was lowered to -15°C, 46.94g of isophthaloyl chloride was added, and the mixture was stirred at a speed of 150rpm. The above process of adding m-phenylenediamine and isophthaloyl chloride was repeated 3 times, wherein an equal amount of isophthaloyl chloride was added each time, and the reaction mixture was stirred at 150rpm for 60min. After the temperature in the autoclave dropped to -15°C, 187.77 g of isophthaloyl chloride was added for the fifth time (the total molar amount of the isophthaloyl chloride added in the first four times was equal to the molar amount of the isophthaloyl chloride added in the fifth time, and the total molar amount of the isophthaloyl chloride added was equal to the molar amount of the m-phenylenediamine); after the reaction was carried out for 1.5 hours, 2 g of m-phenylenediamine was added for end-capping treatment, and the mixture was allowed to stand for 8 hours to obtain the low molecular weight meta-aramid slurry (solid content of 17 wt%, rotational viscosity of 37122 mP·s, inherent viscosity of 1.58 dl / g, and viscosity-average molecular weight of the low molecular weight meta-aramid of 23134);

[0111] Preparation of high molecular weight meta-aramid slurry: 2000g of N,N-dimethylacetamide was added to the reactor, and nitrogen was introduced (the whole process was carried out in a nitrogen atmosphere), and an external cooling circulation system of -30°C was used for cooling. When the temperature dropped to -5°C, 200g of m-phenylenediamine was added, and the mixture was stirred at 150rpm for 60min until the m-phenylenediamine was completely dissolved. The temperature in the reactor was lowered to -15°C, 46.94g of isophthaloyl chloride was added, and the mixture was stirred at a speed of 150rpm. The above process of adding m-phenylenediamine and isophthaloyl chloride was repeated 3 times, wherein an equal amount of isophthaloyl chloride was added each time, and the temperature in the reactor was lowered to 15°C. After the temperature dropped to -15°C, 187.77 g of isophthaloyl chloride was added for the fifth time (the total molar amount of the isophthaloyl chloride added in the first four times was equal to the molar amount of the isophthaloyl chloride added in the fifth time, and the total molar amount of the isophthaloyl chloride added was equal to the molar amount of the m-phenylenediamine); after reacting for 30 minutes, the circulating cooling system was turned off, and the reaction was continued at 300 rpm for 3 hours. Stirring was stopped, and the mixture was allowed to stand for 8 hours to obtain the high molecular weight meta-aramid slurry (solid content of 17 wt%, rotational viscosity of 562354 mP·s, inherent viscosity of 2.38 dl / g, and viscosity-average molecular weight of the high molecular weight meta-aramid of 132638);

[0112] Preparation of ceramic diaphragm: In a room with a dew point of -40°C, 3000 g of the low molecular weight meta-aramid slurry was placed in a reactor and nitrogen was introduced for protection. 15.3 g of aminosilica (accounting for 3% of the solids in the low molecular weight meta-aramid slurry) was added and stirred at 100 rpm for 2 h. 5.1 g of p-phenylene diisocyanate (accounting for 1% of the solids in the low molecular weight meta-aramid slurry) was added and the reaction was continued with stirring for 0.5 h to obtain a ceramic mixed slurry;

[0113] The ceramic mixed slurry and the high molecular weight meta-aramid slurry are mixed to obtain a membrane-forming slurry (the mass ratio of the ceramic mixed slurry to the membrane-forming slurry is 5:100);

[0114] The membrane slurry was sequentially subjected to die extrusion (temperature of 25°C, coat hanger die shape, extrusion pressure of 2 MPa, melt pump speed of 5 rpm), gelation (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretching (stretching ratio of 1.3 times), (water washing temperature of 50°C, time of 3 min), drying (drying temperature of 80°C, time of 2 min) and heat setting (heat setting temperature of 270°C, time of 1 min) to obtain a ceramic diaphragm (thickness of 15 μm);

[0115] Figure 2is the SEM image of the ceramic diaphragm, Figure 2 It can be seen that the silicon dioxide in the ceramic diaphragm is coated.

[0116] Example 2

[0117] Preparation of aminosilica, low molecular weight meta-aramid slurry, high molecular weight meta-aramid slurry, and film-forming slurry as described in Example 1;

[0118] The film-making slurry was extruded through a die (temperature of 25°C, a coat-hanger die shape, an extrusion pressure of 2 MPa, and a melt pump speed of 3.5 rpm) in sequence by non-solvent phase separation, gelled (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretched (the stretching ratio was 1.3 times), (the water washing temperature was 50°C and the time was 3 min), dried (the drying temperature was 80°C and the time was 2 min) and heat-set (the heat-setting temperature was 270°C and the time was 1 min) to obtain a ceramic diaphragm (thickness of 10 μm).

[0119] Example 3

[0120] Preparation of aminosilica and preparation of high molecular weight meta-aramid slurry refer to Example 1;

[0121] Preparation of low molecular weight meta-aramid slurry: 2000g of N,N-dimethylacetamide was added to the reactor, and nitrogen was introduced (the whole process was carried out in a nitrogen atmosphere), and an external cooling circulation system of -30°C was used for cooling. When the temperature dropped to -5°C, 200g of m-phenylenediamine was added, and the m-phenylenediamine was stirred at 150rpm until it was completely dissolved. The temperature in the reactor was lowered to -15°C, 46.94g of isophthaloyl chloride was added, and the stirring speed was 150rpm. The above process of adding m-phenylenediamine and isophthaloyl chloride was repeated 3 times, wherein an equal amount of isophthaloyl chloride was added each time, and the reactor was stirred at 150rpm. After the temperature in the reaction mixture dropped to -15°C, 187.77 g of isophthaloyl chloride was added for the fifth time (the total molar amount of the isophthaloyl chloride added in the first four times was equal to the molar amount of the isophthaloyl chloride added in the fifth time, and the total molar amount of the isophthaloyl chloride added was equal to the molar amount of the m-phenylenediamine); after the reaction was allowed to proceed for 2 hours, 1 g of m-phenylenediamine was added for end-capping treatment, and the mixture was allowed to stand for 8 hours to obtain the low molecular weight meta-aramid slurry (solid content of 17 wt%, rotational viscosity of 37122 mP·s, inherent viscosity of 1.58 dl / g, and viscosity-average molecular weight of the low molecular weight meta-aramid of 42126);

[0122] Preparation of ceramic diaphragm: In a room with a dew point of -40°C, 3000 g of the low molecular weight meta-aramid slurry was placed in a reactor and nitrogen was introduced for protection. 15.3 g of aminosilica (accounting for 3% of the solids in the low molecular weight meta-aramid slurry) was added and stirred at 100 rpm for 2 h. 5.1 g of p-phenylene diisocyanate (accounting for 1% of the solids in the low molecular weight meta-aramid slurry) was added and the reaction was continued with stirring for 0.5 h to obtain a ceramic mixed slurry;

[0123] The ceramic mixed slurry and the high molecular weight meta-aramid slurry are mixed to obtain a membrane-forming slurry (the mass ratio of the ceramic mixed slurry to the membrane-forming slurry is 5:100);

[0124] The film-making slurry was extruded through a die (temperature of 25°C, a coat-hanger die shape, an extrusion pressure of 2 MPa, and a melt pump speed of 5 rpm) in sequence by non-solvent phase separation, gelled (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretched (stretching ratio was 1.3 times), (washing temperature was 50°C, time was 3 min), dried (drying temperature was 80°C, time was 2 min) and heat-set (heat-setting temperature was 270°C, time was 1 min) to obtain a ceramic diaphragm (thickness of 15 μm).

[0125] Example 4

[0126] Preparation of aminosilica and preparation of low molecular weight meta-aramid slurry refer to Example 1;

[0127] Preparation of high molecular weight meta-aramid slurry: 2000g of N,N-dimethylacetamide was added to the reactor, and nitrogen was introduced (the whole process was carried out in a nitrogen atmosphere), and an external cooling circulation system of -30°C was used for cooling. When the temperature dropped to -5°C, 200g of m-phenylenediamine was added, and the mixture was stirred at 150rpm for 60min until the m-phenylenediamine was completely dissolved. The temperature in the reactor was lowered to -15°C, 46.94g of isophthaloyl chloride was added, and the mixture was stirred at a speed of 150rpm. The above process of adding m-phenylenediamine and isophthaloyl chloride was repeated 3 times, wherein an equal amount of isophthaloyl chloride was added each time, and the temperature in the reactor was lowered to 15°C. After the temperature reaches -15°C, 187.77 g of isophthaloyl chloride is added for the fifth time (the total molar amount of the isophthaloyl chloride added in the first four times is equal to the molar amount of the isophthaloyl chloride added in the fifth time, and the total molar amount of the isophthaloyl chloride added is equal to the molar amount of the m-phenylenediamine); after reacting for 10 minutes, the circulating cooling system is turned off, and the reaction is continued at 4500 rpm for 2 hours. Stirring is stopped, and the mixture is allowed to stand for 8 hours to obtain the high molecular weight meta-aramid slurry (solid content of 17 wt%, rotational viscosity of 1735642 mP·s, inherent viscosity of 3.05 dl / g, and viscosity-average molecular weight of the high molecular weight meta-aramid of 166235);

[0128] Preparation of ceramic diaphragm: In a room with a dew point of -40°C, 3000 g of the low molecular weight meta-aramid slurry was placed in a reactor and nitrogen was introduced for protection. 15.3 g of aminosilica (accounting for 3% of the solids in the low molecular weight meta-aramid slurry) was added and stirred at 100 rpm for 2 h. 5.1 g of p-phenylene diisocyanate (accounting for 1% of the solids in the low molecular weight meta-aramid slurry) was added and the reaction was continued with stirring for 0.5 h to obtain a ceramic mixed slurry;

[0129] The ceramic mixed slurry and the high molecular weight meta-aramid slurry are mixed to obtain a membrane-forming slurry (the mass ratio of the ceramic mixed slurry to the membrane-forming slurry is 5:100);

[0130] The film-making slurry was extruded through a die (temperature of 25°C, a coat-hanger die shape, an extrusion pressure of 2 MPa, and a melt pump speed of 5 rpm) in sequence by non-solvent phase separation, gelled (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretched (stretching ratio was 1.3 times), (washing temperature was 50°C, time was 3 min), dried (drying temperature was 80°C, time was 2 min) and heat-set (heat-setting temperature was 270°C, time was 1 min) to obtain a ceramic diaphragm (thickness of 15 μm).

[0131] Example 5

[0132] Preparation of aminosilica, low molecular weight meta-aramid slurry, and high molecular weight meta-aramid slurry Reference Example 1;

[0133] Preparation of ceramic diaphragm: In a room with a dew point of -40°C, 3000 g of the low molecular weight meta-aramid slurry was placed in a reactor and nitrogen was introduced for protection. 51 g of aminosilica (accounting for 10% of the solids in the low molecular weight meta-aramid slurry) was added and stirred at 100 rpm for 2 h. 5.1 g of p-phenylene diisocyanate (accounting for 1% of the solids in the low molecular weight meta-aramid slurry) was added and the reaction was continued with stirring for 0.5 h to obtain a ceramic mixed slurry;

[0134] The ceramic mixed slurry and the high molecular weight meta-aramid slurry are mixed to obtain a membrane-forming slurry (the mass ratio of the ceramic mixed slurry to the membrane-forming slurry is 5:100);

[0135] The film-making slurry was extruded through a die (temperature of 25°C, a coat-hanger die shape, an extrusion pressure of 2 MPa, and a melt pump speed of 5 rpm) in sequence by non-solvent phase separation, gelled (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretched (stretching ratio was 1.3 times), (washing temperature was 50°C, time was 3 min), dried (drying temperature was 80°C, time was 2 min) and heat-set (heat-setting temperature was 270°C, time was 1 min) to obtain a ceramic diaphragm (thickness of 15 μm).

[0136] Example 6

[0137] Preparation of aminosilica, low molecular weight meta-aramid slurry, and high molecular weight meta-aramid slurry Reference Example 1;

[0138] Preparation of ceramic diaphragm: In a room with a dew point of -40°C, 3000 g of the low molecular weight meta-aramid slurry was placed in a reactor and nitrogen was introduced for protection. 15.3 g of aminosilica (accounting for 10% of the solids in the low molecular weight meta-aramid slurry) was added and stirred at 100 rpm for 2 h. 15.3 g of p-phenylene diisocyanate (accounting for 3% of the solids in the low molecular weight meta-aramid slurry) was added and the reaction was continued with stirring for 0.5 h to obtain a ceramic mixed slurry;

[0139] The ceramic mixed slurry and the high molecular weight meta-aramid slurry are mixed to obtain a membrane-forming slurry (the mass ratio of the ceramic mixed slurry to the membrane-forming slurry is 5:100);

[0140] The film-making slurry was extruded through a die (temperature of 25°C, a coat-hanger die shape, an extrusion pressure of 2 MPa, and a melt pump speed of 5 rpm) in sequence by non-solvent phase separation, gelled (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretched (stretching ratio was 1.3 times), (washing temperature was 50°C, time was 3 min), dried (drying temperature was 80°C, time was 2 min) and heat-set (heat-setting temperature was 270°C, time was 1 min) to obtain a ceramic diaphragm (thickness of 15 μm).

[0141] Example 7

[0142] Preparation of aminosilica, low molecular weight meta-aramid slurry, and high molecular weight meta-aramid slurry Reference Example 1;

[0143] Preparation of ceramic diaphragm: In a room with a dew point of -40°C, 3000 g of the low molecular weight meta-aramid slurry was placed in a reactor and nitrogen was introduced for protection. 15.3 g of aminosilica (accounting for 10% of the solids in the low molecular weight meta-aramid slurry) was added and stirred at 100 rpm for 2 h. 15.3 g of p-phenylene diisocyanate (accounting for 3% of the solids in the low molecular weight meta-aramid slurry) was added and the reaction was continued with stirring for 0.5 h to obtain a ceramic mixed slurry;

[0144] Mixing the ceramic mixed slurry and the high molecular weight meta-aramid slurry to obtain a membrane-forming slurry (the mass ratio of the ceramic mixed slurry to the membrane-forming slurry is 10:100);

[0145] The film-making slurry was extruded through a die (temperature of 25°C, a coat-hanger die shape, an extrusion pressure of 2 MPa, and a melt pump speed of 5 rpm) in sequence by non-solvent phase separation, gelled (the non-solvent in the gel tank was water, the solvent was DMAC, and the mass ratio of the non-solvent to the solvent was 3:7), stretched (stretching ratio was 1.3 times), (washing temperature was 50°C, time was 3 min), dried (drying temperature was 80°C, time was 2 min) and heat-set (heat-setting temperature was 270°C, time was 1 min) to obtain a ceramic diaphragm (thickness of 15 μm).

[0146] Comparative Example 1

[0147] Refer to Example 1, except that low molecular weight meta-aramid slurry is not prepared, and the membrane-making slurry does not include aminosilica, and the membrane-making slurry is only high molecular weight meta-aramid slurry; a ceramic diaphragm (thickness of 15 μm) is obtained.

[0148] Comparative Example 2

[0149] Refer to Example 1, except that amino silica is not prepared. The preparation process of the ceramic diaphragm is as follows: the low molecular weight meta-aramid slurry and the high molecular weight meta-aramid slurry are mixed to obtain a membrane-forming slurry (the mass ratio of the low molecular weight meta-aramid slurry to the membrane-forming slurry is 5:100); and a ceramic diaphragm (with a thickness of 15 μm) is obtained.

[0150] Comparative Example 3

[0151] Refer to Example 1, except that aminosilica is not prepared, and aminosilica is replaced by ordinary silicon dioxide to obtain a ceramic diaphragm (with a thickness of 15 μm).

[0152] Comparative Example 4

[0153] Referring to Example 1, the only difference is that the mass ratio of the ceramic mixed slurry to the film-forming slurry is 20: 100. The film-forming slurry prepared by this solution is easily broken during stretching during the film-forming process and cannot be wound up.

[0154] Test Case

[0155] Preparation of secondary lithium-free negative electrode button cells: A lithium metal with a diameter of 15.8 mm was used as the negative electrode, a copper foil with a thickness of 8 μm and a diameter of 13 mm was used as the positive electrode, and the ceramic separators described in Examples 1 to 7 and Comparative Examples 1 to 4 were respectively made into separators with a diameter of 19 mm. A commercial Y1 electrolyte was used as the electrolyte, and 2032-size button cells were assembled in a glove box filled with argon (O<0.01 ppm, H<0.01 ppm).

[0156] The 2032 model button battery was tested: after the 2032 model button battery was left to stand for 24 hours, it was placed on a blue electric test cabinet, and according to the amount of lithium deposition per square centimeter 3mA·h, it was first discharged at a constant current of 0.3C, 0.398mA to a capacity of 3.98mA·h, and then charged at a constant current of 0.3C, 0.398mA to 1.5V, and the above charge and discharge process was repeated for 3 cycles, and then discharged at a constant current of 1C, 1.33mA to a capacity of 3.98mA·h, and then charged at a constant current of 1C, 1.33mA. This step is one button cycle; the changes in the number of cycles and the discharge specific capacity value were recorded. The results are as follows Figures 3-4 As shown, Figure 3 This is the cycle performance curve of the 2032-type button battery prepared with the ceramic diaphragm described in Example 1. Figure 4 The cycle performance curve of the 2032 button battery prepared by the ceramic diaphragm described in Comparative Example 1 is shown in FIG. Figure 1It can be seen that the cycle performance of the secondary lithium-free negative electrode button battery prepared by the ceramic diaphragm described in Example 1 is significantly improved compared with the secondary lithium-free negative electrode button battery prepared by the ceramic diaphragm described in Comparative Example 1, and the number of cycles is significantly increased;

[0157] The number of cycles of the secondary lithium-free negative electrode button cells prepared with the ceramic diaphragms described in Examples 1 to 7 and Comparative Examples 1 to 3 when short-circuited during the cycle performance test is shown in Table 1:

[0158] The ceramic diaphragms described in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to puncture strength tests. The test results are shown in Table 1.

[0159] The ceramic diaphragms described in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to thermal shrinkage tests, and the test results are shown in Table 1;

[0160] Table 1 Performance parameters of the ceramic diaphragms described in Examples 1 to 7 and Comparative Examples 1 to 3

[0161]

[0162] It can be seen from Table 1 that in the ceramic diaphragm, amino silica, low molecular weight meta-aramid and high molecular weight meta-aramid are three indispensable materials. If any one of the materials is missing, the puncture strength, thermal shrinkage and number of cycles during short circuit are all poor. Furthermore, according to the analysis of Examples 1 to 7 and Comparative Example 3, since Comparative Document 3 replaces amino silica with ordinary silica, it is impossible to achieve the coating of low molecular weight meta-aramid, resulting in the inability to improve its puncture strength, thermal shrinkage and number of cycles during short circuit. It can be seen that the reason why the ceramic diaphragm described in the present invention has significantly improved puncture performance, thermal shrinkage performance and cycle stability is that the amino silica in the ceramic diaphragm described in the present invention is cross-linked with the low molecular weight meta-aramid through a cross-linking agent to form an interactive coating composite material; the cross-linking agent cross-links the amino silica with the amino groups in the low molecular weight meta-aramid to form a coating layer, and the low molecular weight meta-aramid end groups have relatively more amino groups, and the amino groups in the amino silica form tighter cross-links with the end groups of the low molecular weight meta-aramid, and the addition of high molecular weight meta-aramid provides sufficient membrane strength for the diaphragm.

[0163] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A ceramic diaphragm, characterized in that: The materials of the ceramic diaphragm include aminosilica, low molecular weight meta-aramid and high molecular weight meta-aramid; The low molecular weight meta-aramid is coated on the surface of the aminosilica through a cross-linking agent; The high molecular weight meta-aramid and the low molecular weight meta-aramid are connected in a molecular entanglement manner; The viscosity average molecular weight of the low molecular weight meta-aramid is 1 to 7W; The viscosity average molecular weight of the high molecular weight meta-aramid is 10-20W.

2. The ceramic diaphragm according to claim 1, characterized in that The high molecular weight meta-aramid is not connected to aminosilica; Or part of the high molecular weight meta-aramid fiber is connected to aminosilica via a crosslinking agent.

3. The ceramic diaphragm according to claim 1 or 2, characterized in that The cross-linking agent is an isocyanate compound containing two or more isocyanate groups; The isocyanate groups in the isocyanate compound are cross-linked with the amino groups in the aminosilica and the amino groups in the low molecular weight meta-aramid respectively; Or the isocyanate group in the isocyanate compound is cross-linked with the amino group in the aminosilica, the amino group in the low molecular weight meta-aramid, or the amino group in the high molecular weight meta-aramid.

4. The ceramic diaphragm according to claim 3, characterized in that The crosslinking agent includes one or more of p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthalene 1,5-diisocyanate, p-phenylene diisocyanate and triphenylmethane triisocyanate.

5. The ceramic diaphragm according to any one of claims 1 to 4, characterized in that: The low molecular weight meta-aramid slurry for preparing the ceramic diaphragm has a solid content of 12 to 20 wt%, a rotational viscosity of 10,000 to 90,000 mP·s, and an inherent viscosity of 1.3 to 1.8 dl / g; The high molecular weight meta-aramid slurry for preparing the ceramic diaphragm has a solid content of 12-20 wt%, a rotational viscosity of 200,000-2,000,000 mP·s, and an inherent viscosity of 2.3-3.2 dl / g.

6. The ceramic diaphragm according to claim 5, characterized in that The preparation method of the low molecular weight meta-aramid slurry comprises the following steps: Under protective atmosphere, stirring and circulating cooling conditions, the first m-phenylenediamine and isophthaloyl chloride are sequentially added to N,N-dimethylacetamide, the above process of adding the isophthaloyl chloride is repeated three times, the isophthaloyl chloride is added for the fifth time, and the second m-phenylenediamine is added for end-capping treatment to obtain the low molecular weight meta-aramid slurry; The end-capping treatment is carried out under static conditions, and the time of the end-capping treatment is 5 to 8 hours.

7. The ceramic diaphragm according to claim 5, characterized in that The preparation method of the high molecular weight meta-aramid slurry comprises the following steps: Under the conditions of protective atmosphere, stirring and circulating cooling, the first m-phenylenediamine and isophthaloyl chloride are added to N,N-dimethylacetamide in sequence, and the above process of adding the isophthaloyl chloride is repeated three times. Then, isophthaloyl chloride is added for the fifth time, and the reaction is continued under circulating cooling, the circulating cooling is stopped and the reaction is continued, and the reaction is allowed to stand, thereby obtaining the high molecular weight m-aramid slurry.

8. The method for preparing the ceramic diaphragm according to any one of claims 1 to 7, characterized in that: The following steps are involved: After mixing low molecular weight meta-aramid slurry and amino silica, a cross-linking agent is added to obtain a ceramic mixed slurry; Mixing the ceramic mixed slurry and high molecular weight meta-aramid slurry to obtain a membrane-making slurry; The membrane-forming slurry is formed into a membrane to obtain the ceramic separator.

9. The preparation method according to claim 8, wherein The low molecular weight meta-aramid slurry and aminosilica are mixed in a protective atmosphere at a dew point of -40°C to -60°C. The mixing is carried out under stirring conditions, the stirring speed is 100 to 500 rpm, and the time is 1 to 6 hours; The mass ratio of the aminosilica to the low molecular weight meta-aramid slurry is (0.5-10):

100.

10. The preparation method according to claim 8, characterized in that The mass ratio of the p-phenylene diisocyanate to the low molecular weight meta-aramid slurry is (0.1-5):100; The mass ratio of the ceramic mixed slurry to the membrane-forming slurry is (0.5-10):

100.

11. Use of the ceramic diaphragm according to any one of claims 1 to 7 or the ceramic diaphragm prepared by the preparation method according to any one of claims 8 to 10 in a secondary lithium battery.

12. The use according to claim 11, characterized in that The secondary lithium battery is a secondary lithium-free negative electrode battery.

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