Large-through-flow varistor and preparation method thereof

Abstract

The invention discloses a large-through-flow varistor and a preparation method thereof, and belongs to the technical field of varistors, the varistor is prepared from the following raw materials: 93 to 96 mol percent of modified ZnO, 1.2 to 1.6 mol percent of Bi2O3, 0.5 to 1.5 mol percent of Co3O4, 0.3 to 0.8 mol percent of Mn2O3, 1.0 to 3.0 mol percent of Sb2O3, 0.3 to 0.8 mol percent of NiO and 0.05 to 0.3 mol percent of Li2CO3; a silane coupling agent with a fluorinated quaternary ammonium salt structure is adopted to modify the surface of ZnO, and the quaternary ammonium salt structure improves the isoelectric point of ZnO, so that ZnO is positively charged at a relatively high pH value, the interaction with an anionic dispersant is enhanced, and the effect of the anionic dispersant on slurry is improved; f <-> introduced by the silane coupling agent is uniformly dispersed on the surface of ZnO, during subsequent sintering, Li < + > is used as a diffusion carrier, the migration rate of F <-> in crystal lattices can be improved through the synergistic effect of Li < + > and F <->, and the property of the ZnO varistor is enhanced by introducing Li < + > and F <->.

Description

Technical Field

[0001] The present invention belongs to the technical field of varistors, and particularly relates to a large-current varistor chip and a preparation method thereof. Background Art

[0002] ZnO varistors are a new type of multifunctional semiconductor ceramic component mainly made of ZnO, doped with a small amount of other metal oxides (such as Bi2O3, Sb2O3, Co3O4, Ni2O3, SiO2, etc.), and sintered by traditional ceramic processes. ZnO varistors are widely used in high-voltage and low-voltage power systems, rail transit, facility protection and other fields because of their advantages such as cheap raw materials, simple process, adjustable potential gradient, high non-linear coefficient, low voltage ratio, and long operation time in the circuit. Large-current ZnO varistors are smaller in volume, saving raw material costs, more convenient during transportation and use, and the miniaturization of the equipment used conforms to the current development trend. At present, the trend in preparing high-gradient non-linear resistors is to dope rare-earth oxides. Compared with other common metal oxides, rare-earth oxides are more expensive, and high-quality high-gradient resistor chips on the market are basically monopolized by foreign countries, and the high price has become a key restrictive factor. However, excellent non-linear resistor performance can be finally obtained by optimizing the formula and process.

[0003] The key technologies in the preparation of ZnO varistors lie in the formula and the uniformity of the ceramic body. The uniformity of the ceramic body directly affects the electrical properties of the finished product. In the formula of ZnO varistors, doping mainly includes donor doping and acceptor doping. Donor doping can be divided into rare-earth element doping and transition metal oxide doping, and acceptor doping mainly includes monovalent ions, such as: Li + 、Na + 、K + 、Ag + etc. Among them, the radius of lithium ions is slightly smaller than that of zinc ions. Lithium ions enter the ZnO lattice, changing the electrical parameters of grains and grain boundaries. Trace Li + doping can improve the non-linear coefficient and leakage current. At present, there are few reports on fluoride ions doped into zinc oxide as anions, mainly due to the dispersion of fluoride ions and their influence on other doped oxides. Well-dispersed slurries are the key factors for obtaining dense green bodies, uniform microstructures and additive distributions, and minimal defects, and finally obtaining excellent non-linear resistors. Among them, the content of the dispersant is the key factor for the slurry to have good fluidity and dispersibility. Summary of the Invention

[0004] The present invention provides a large-current varistor chip and a preparation method thereof, using a silane coupling agent with a quaternary ammonium fluoride structure to modify the surface of ZnO, introducing more positive charges and introducing F -, the quaternary ammonium salt structure increases the isoelectric point of ZnO, making it have more positive charges even at higher pH values, enhancing the interaction with anionic dispersants and strengthening the dispersion stability of the anionic dispersant for the slurry; F introduced through the silane coupling agent - uniformly disperses on the surface of ZnO. During subsequent sintering, using Li + as the diffusion carrier, the synergistic effect of Li + and F - can improve the mobility of F - in the lattice. Introducing Li + and F - enhances the properties of ZnO varistors.

[0005] The technical solution to achieve the object of the present invention is as follows: A preparation method of a large-current varistor chip, comprising the following steps:

[0006] S1. ZnO surface modification: Add ZnO to a solution containing deionized water and ethanol, add a silane coupling agent with a fluorinated quaternary ammonium salt structure, and stir to obtain modified ZnO;

[0007] S2. Configure the raw materials for preparing the varistor chip: 93-96 mol% of modified ZnO, 1.2-1.6 mol% of Bi2O3, 0.5-1.5 mol% of Co3O4, 0.3-0.8 mol% of Mn2O3, 1.0-3.0 mol% of Sb2O3, 0.3-0.8 mol% of NiO, and 0.05-0.3 mol% of Li2CO3;

[0008] S3. Mix the additives except modified ZnO and Li2CO3, add deionized water and an anionic dispersant to form an additive slurry, grind it in a sand mill, dry and crush it to obtain an additive powder. Mix ZnO, Li2CO3 and the additive powder, add deionized water, an anionic dispersant and a binder, and grind and refine it in a ball mill to obtain a total slurry;

[0009] S4. Spray granulate the total slurry, carry out water-containing aging and dry pressing to form a blank. Subject the dry-pressed blank to degumming treatment, then sinter it at a high temperature, grind and level it, and then perform heat treatment. Coat silver electrodes on the upper and lower ends, and coat insulating glaze on the side to obtain a varistor;

[0010] The degumming treatment operation is as follows:

[0011] In an inert atmosphere, in a closed system, at 150 °C, put in the blank, heat it up to 300 °C at a rate of 2-5 °C / min for treatment, keep it warm for 0.5-1 h, and then, under an open system, treat it at 300-450 °C for 1-2 h;

[0012] The structure of the silane coupling agent with a fluorinated quaternary ammonium salt structure is as shown below:

[0013] In the formula, at least one of R1, R2, R3, R4, R5 and R6 is methyl or ethyl.

[0014] The mechanism of the present invention is mainly as follows. As shown in the attached Figure 1 figure, the surface of zinc oxide is modified by a silane coupling agent with a fluorinated quaternary ammonium salt structure, introducing additional cationic groups to enhance the interaction with anions. At the same time, F is - uniformly dispersed on the surface of ZnO. At 200 - 500 °C, the quaternary ammonium salt structure decomposes slowly, and F - and Li + form LiF or ZnF2 on the surface of ZnO. With the increase of temperature for calcination, F - and Li + enter the ZnO lattice, changing the electrical parameters of grains and grain boundaries.

[0015] Preferably, in step S1, the ratio of water to ethanol is 1:3 - 1:5, the mass ratio of the silane coupling agent to ZnO is (0.3 - 0.8):(99.2 - 99.7), the reaction temperature is 30 - 60 °C, and the reaction time is at least 1 h.

[0016] Preferably, in step S3, the solid content of the additive slurry is 20 - 50 wt.%, the addition amount of the anionic dispersant of the additive powder is 0.1 - 1 wt.% of the additive, and it is sanded until the particle size of the mixed slurry is 400 - 600 nm; the amount of the anionic dispersant in the total slurry is 0.1 - 1 wt.% of the total mass of the powder, the amount of the binder is 0.5 - 1 wt.% of the total mass of the powder, the ball milling time is 20 - 24 h, the binder is polyvinyl alcohol, and the anionic dispersant is an ammonium polyacrylate dispersant.

[0017] Preferably, in step S4, the moisture aging means testing the moisture content of the granulated powder and adjusting the moisture content according to the measurement results to make the moisture content of the granulated powder 1.2 - 2%.

[0018] Preferably, in step S4, the high - temperature sintering step is to heat up to 800 - 900 °C at a heating rate of 1.5 - 2.0 °C / min, and then heat up to 1000 - 1200 °C at a heating rate of 0.5 - 1.0 °C / min, keep it warm for 1.5 - 2.5 h and then cool down with the furnace; the heat treatment temperature is 400 - 600 °C and keep it warm for 1 - 2 h.

[0019] Preferably, the preparation method of the silane coupling agent with a fluorinated quaternary ammonium salt structure is as follows:

[0020] Disperse 1 eq of ammonium salt silane coupling agent and at least 5 eq of potassium fluoride in methanol, stir at 20 - 30 °C for 40 - 80 min, filter to remove the solid, remove most of the solvent by rotary evaporation, add dichloromethane, wash the organic phase with deionized water, and remove the solvent to obtain the silane coupling agent with a fluorinated quaternary ammonium salt structure.

[0021] The ammonium salt silane coupling agent is one or more of 3-triethoxysilylpropyltrimethylammonium chloride, 3-triethoxysilylpropyltrimethylammonium bromide, 3-triethoxysilylpropyltriethylammonium chloride, 3-triethoxysilylpropyltriethylammonium bromide, 3-trimethoxysilylpropyltrimethylammonium chloride, 3-trimethoxysilylpropyltrimethylammonium bromide, 3-trimethoxysilylpropyltriethylammonium chloride, and 3-trimethoxysilylpropyltriethylammonium bromide.

[0022] Preferably, the ammonium salt silane coupling agent is 3-triethoxysilylpropyltrimethylammonium chloride.

[0023] The present invention also discloses a high-current varistor chip obtained by the preparation method of a high-current varistor chip as described above.

[0024] Beneficial effects

[0025] The present invention has the following beneficial effects: providing a high-current varistor chip and its preparation method, the slurry of the varistor chip has a lower viscosity and good dispersibility; using a silane coupling agent to modify zinc oxide, firstly introducing a quaternary ammonium salt cation with weak pH sensitivity, improving the interaction with anionic dispersants, and secondly uniformly dispersing F - onto the ZnO surface without affecting other additives; doping with trace amounts of Li + while increasing the non-linear coefficient and leakage current, improving the mobility of F - in the lattice; introducing F - plays a role in inhibiting grain growth, generating finer and more uniform grains; F - substituting O 2- can change the charge distribution at the grain boundary, increase the barrier height, improve the non-linear coefficient, and reduce the leakage current; the incorporation of an appropriate amount of F - can stabilize the lattice structure, reduce the generation of oxygen vacancies at high temperatures, thereby delaying material aging and extending the device life. Description of the drawings

[0026] Figure 1 Steps for modifying the ZnO surface with a quaternized silane coupling agent and the mechanism of action with an anionic dispersant. Detailed implementation manners

[0027] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0028] In the embodiments, unless otherwise specified, the experimental methods used are all conventional methods, and the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels.

[0029] The raw materials and equipment used in the examples and comparative examples are described as follows:

[0030] 3-triethoxysilylpropyltrimethylammonium chloride: Luoen reagent;

[0031] Potassium fluoride: ≥99.97%, Shanghai Aladdin;

[0032] ZnO: varistor grade, Nantong Jinqi Chemical Co., Ltd.;

[0033] Bi2O3: electronic grade, Shanghai Jiujia Powder Materials Co., Ltd.;

[0034] Sb2O3: electronic grade, Chengdu Dayu Functional Materials Co., Ltd.;

[0035] Mn2O3: electronic grade, Chengdu Dayu Functional Materials Co., Ltd.;

[0036] Co3O4: electronic grade, Shanghai Jiujia Powder Materials Co., Ltd.;

[0037] NiO: electronic grade, Shanghai Jiujia Powder Materials Co., Ltd.;

[0038] Polyvinyl alcohol: PVA-1788, industrial grade, Shanghai Petrochemical Co., Ltd.;

[0039] Release agent: HDA-80 type ceramic lubricant, Xi'an Xinzheng Electronic Materials Co., Ltd.;

[0040] Anionic dispersant: D-134 dispersant, Daiichi Kogyo Seiyaku Co., Ltd. of Japan;

[0041] 3-aminopropyltriethoxysilane: Shanghai Aladdin;

[0042] Li2CO3: 99.999%, Luoen reagent;

[0043] LiF: 99.99%, Luoen reagent.

[0044] Silane coupling agent 1

[0045] Disperse 1 eq of 3-triethoxysilylpropyltrimethylammonium chloride and 15 eq of potassium fluoride in methanol, stir at 30 °C for 60 min, filter to remove the solid, after rotary evaporation to remove most of the solvent, add dichloromethane, wash the organic phase with deionized water, and remove the solvent to obtain silane coupling agent 1.

[0046] Silane coupling agent 2

[0047] Use 3-triethoxysilylpropyltrimethylammonium chloride.

[0048] Silane coupling agent 3

[0049] Use 3-aminopropyltriethoxysilane.

[0050] Example 1

[0051] S1. ZnO surface modification: Add 997 g of ZnO to a solution containing deionized water and ethanol, where the volume ratio of deionized water to ethanol is 1:3, add 3 g of silane coupling agent 1, and stir at 40 °C for 2 h to obtain quaternized ZnO;

[0052] S2. Prepare the raw materials for the varistor chip: Modified ZnO 94.60 mol%, Bi2O3 1.45 mol%, Co3O4 0.55 mol%, Mn2O3 0.51 mol%, Sb2O3 2.10 mol%, NiO 0.52 mol%, and Li2CO3 0.27 mol%;

[0053] S3. Mix the additives except modified ZnO and Li2CO3, add deionized water and anionic dispersant to prepare an additive slurry with a solids content of 20 wt.%, the addition amount of the anionic dispersant is 0.4 wt.% of the total powder mass, and use Horizontal sand mill to grind at a main machine speed of 1000 rpm, a feed pump speed of 30 rpm, and circulate once until the particle size of the mixed slurry is 500 nm. After the grinding is completed, dry and pulverize, and after obtaining the additive powder, mix ZnO, Li2CO3, and the additive powder, add deionized water, anionic dispersant, and binder to a polyurethane ball mill tank. The dosage of the anionic dispersant is 0.4 wt.% of the total powder mass, and the dosage of the binder is 0.8 wt.% of the total powder mass. Use agate balls as the grinding medium (powder: deionized water: agate balls = 1:0.65:2.4), and use a ball mill (GMJ-8-5, Wuxi Hengguang Powder Equipment Co., Ltd.) to carry out ball milling and refining treatment at a speed of 400 r / min for 24 h to obtain the total slurry;

[0054] S4. The total slurry is spray granulated using an industrial high-speed centrifugal spray dryer. The inlet air temperature of the equipment is 220 °C, the outlet air temperature is 110 °C, and the rotational speed of the atomizer is 40 Hz. The actual moisture content of the spray granulated powder is tested. With the target of the powder moisture content being 1.6 wt.%, a certain amount of deionized water is added to increase the moisture content. At the same time, a mold release agent accounting for 0.7 wt.% of the powder mass is added to assist the dry pressing of the powder. After mixing the two, they are evenly sprayed on the powder and sealed and left standing for 20 h. Dry pressing: A two-way powder hydraulic press (Y79-25, Shanghai Huchi Electric Appliance Development Co., Ltd.) is used for dry pressing. The density of the circular green body obtained by pressing is about 3.20 g / cm 3 or so. The green body obtained by dry pressing is subjected to debinding treatment: In an inert atmosphere and a closed system, it is heated from 150 °C to 300 °C at a rate of 2 - 5 °C / min and treated for 1 h. Then, under an open system, it is treated at 450 °C for 2 h. Then high-temperature sintering: High-temperature sintering is carried out using a muffle furnace at 1100 °C and kept warm for 1.5 h. After grinding and leveling, heat treatment (kept warm at 550 °C for 180 min) is performed, silver electrodes are coated on the upper and lower end faces, and insulating glaze is coated on the side surfaces to obtain a varistor.

[0055] Example 2

[0056] Compared with the preparation method of Example 1, the difference lies in that in step S1, 997 g of ZnO is replaced with 995 g of ZnO, and 3 g of silane coupling agent 1 is replaced with 5 g of silane coupling agent 1.

[0057] Example 3

[0058] Compared with the preparation method of Example 1, the difference lies in that in step S1, 997 g of ZnO is replaced with 992 g of ZnO, and 3 g of silane coupling agent 1 is replaced with 8 g of silane coupling agent 1.

[0059] Comparative Example 1

[0060] Compared with the preparation method of Example 1, the difference lies in that the surface modification of ZnO in step S1 is not carried out, and the modified ZnO in step S2 is replaced with ZnO.

[0061] Comparative Example 2

[0062] Compared with the preparation method of Example 1, the difference lies in that in step S1, 3 g of silane coupling agent 1 is replaced with 3 g of silane coupling agent 2.

[0063] Comparative Example 3

[0064] Compared with the preparation method of Example 1, the difference lies in that in step S1, 3 g of silane coupling agent 1 is replaced with 3 g of silane coupling agent 3.

[0065] Comparative Example 4

[0066] Compared with the preparation method of Example 1, the difference lies in that in step S1, 997 g of ZnO is replaced with 985 g of ZnO, and 3 g of silane coupling agent 1 is replaced with 15 g of silane coupling agent 1.

[0067] Comparative Example 5

[0068] Compared with the preparation method of Example 1, the difference lies in that in steps S2 and S3, 0.27 mol% of Li2CO3 is replaced with 0.27 mol% of modified ZnO.

[0069] Comparative Example 6

[0070] Compared with the preparation method of Example 1, the difference lies in that the surface modification of ZnO in step S1 is not carried out, the modified ZnO in step S2 is replaced with ZnO, and in steps S2 and S3, 0.27 mol% of Li2CO3 is replaced with 0.27 mol% of LiF.

[0071] The following are the test methods for the performance parameters involved in the present invention:

[0072] Total slurry viscosity: Measured using a Shanghai Changji NDJ-8S type rotary viscometer;

[0073] Grain size: SEM characterization is carried out on the upper surface of the resistor chip;

[0074] Nonlinear coefficient of ZnO varistor: α = 1 / log l0 (U 1mA / U 0.1mA ), where: α is the nonlinear coefficient; U 0.1mA is the voltage value of the varistor at 0.1 mA DC, kV;

[0075] Residual voltage ratio: The resistor chip is subjected to an 8 / 20 μs lightning impulse current simulation test by an impulse current testing machine, and the residual voltage value U 5kA is measured after the resistor chip passes through a 5 kA impulse current, so as to calculate the residual voltage ratio, and the residual voltage ratio of the varistor is calculated: K 5kA =U 5kA / U 1mA , where: K 5kA is the residual voltage ratio at 5 kA lightning current; U 5kA is the residual voltage of the varistor passing through 8 / 20 μs;

[0076] Aging coefficient: The resistor chip is subjected to an accelerated aging test using an AC / DC aging machine, and the test conditions are continuous operation at 135 °C and 85% U 1mA voltage for 96 h, and the aging coefficient K ct =P 96h / P 1h , P 96his the power for 96h, P 1h is the power for 1h, K ct The smaller it is, the better the aging resistance.

[0077] Table 1 Total Slurry Viscosity and Electrical Properties of Varistors

[0078] Total slurry viscosity (mpa·s) Grain size (μm) Nonlinear coefficient Aging coefficient Residual voltage ratio Example 1 38.5 5.67 65.6 0.87 1.461 Example 2 35.8 5.40 67.5 0.85 1.441 Example 3 32.9 5.58 66.2 0.88 1.450 Comparative example 1 59.1 6.97 55.1 1.25 1.680 Comparative example 2 40.5 6.58 59.1 1.14 1.631 Comparative example 3 54.1 6.55 58.5 1.15 1.645 Comparative example 4 27.6 6.38 60.2 1.10 1.608 Comparative example 5 39.1 5.99 62.8 1.04 1.563 Comparative example 6 60.8 7.19 53.2 1.35 1.729

[0079] From the performance tests of the examples and comparative examples, it can be seen that within a suitable range, using a silane coupling agent with a fluorinated quaternary ammonium salt structure to modify the surface of ZnO can obtain varistors with excellent performance.

[0080] From the data of Examples 1 - 3 and Comparative Example 4 in Table 1, as the amount of the silane coupling agent with a fluorinated quaternary ammonium salt structure modifying ZnO increases, the total slurry viscosity gradually decreases, but the electrical properties first increase and then decrease. The gradual decrease in the total slurry viscosity is due to the introduction of more cationic groups, and the reasons for the first increase and then decrease in electrical properties may be: 1) Excessive F - will lead to too many defects; 2) Poor dispersibility and uneven dispersion; 3) The probability of reaction with other dopants increases. From the data of Comparative Example 2, it can be seen that when using a silane coupling agent with a chlorinated quaternary ammonium structure, the total slurry viscosity is close to that of Example 1, but the electrical properties are not as good as those of Examples 1 - 3, indicating that F - has a better effect on the electrical properties of varistors than Cl - . From the data of Comparative Example 3, it can be seen that without using a silane coupling agent with a quaternary ammonium salt structure, both the total slurry viscosity and the electrical properties are not as good as those of Examples 1 - 3. From the data of Comparative Example 5, it can be seen that without adding Li2CO3, the impact on the performance of the total slurry viscosity is relatively small, but it has a greater impact on the electrical properties of the varistor, resulting in its performance being inferior to that of the examples; from the data of Comparative Example 6, it can be seen that directly adding LiF will cause a decrease in both the total slurry viscosity and the electrical properties of the varistor, proving that the dispersion of LiF in the slurry has a greater impact on the electrical properties of the varistor.

[0081] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can better understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation method of a large-current varistor chip, characterized in that, It includes the following steps: S1. ZnO surface modification: Add ZnO into a solution containing deionized water and ethanol, add a silane coupling agent with a quaternary ammonium fluoride structure, and stir to obtain modified ZnO; S2. Prepare the raw materials for manufacturing the varistor chip: 93 - 96 mol% of modified ZnO, 1.2 - 1.6 mol% of Bi2O3, 0.5 - 1.5 mol% of Co3O4, 0.3 - 0.8 mol% of Mn2O3, 1.0 - 3.0 mol% of Sb2O3, 0.3 - 0.8 mol% of NiO, and 0.05 - 0.3 mol% of Li2CO3; S3. Mix the additives except modified ZnO and Li2CO3, add deionized water and an anionic dispersant to form an additive slurry, grind it in a sand mill, dry and crush it to obtain an additive powder. Mix ZnO, Li2CO3 and the additive powder, add deionized water, an anionic dispersant and a binder, and refine it by ball milling in a ball mill to obtain a total slurry; S4. Spray granulate, age with water content and dry press the total slurry. Debind the dry - pressed green body, then sinter it at a high temperature, grind and level it, and then perform heat treatment. Coat silver electrodes on the upper and lower ends, and coat insulating glaze on the side to obtain a varistor; The debinding treatment operation is as follows: Inert atmosphere, closed system. Put the green body at 150 °C, heat it up to 300 °C at a rate of 2 - 5 °C / min for treatment, keep it warm for 0.5 - 1 h, and then, under an open system, treat it at 300 - 450 °C for 1 - 2 h; The structure of the silane coupling agent with a quaternary ammonium fluoride structure is as follows: Wherein, R1, R2, R3, R4, R5 and R6 are at least one of methyl and ethyl.

2. The preparation method of a large-current varistor chip according to claim 1, characterized in that In step S1, the ratio of water to ethanol is 1:3 - 1:5, the mass ratio of the silane coupling agent to ZnO is (0.3 - 0.8):(99.2 - 99.7), the reaction temperature is 30 - 60 °C, and the reaction time is at least 1 h.

3. The preparation method of a large-current varistor chip according to claim 1, characterized in that, In step S3, the solid content of the additive slurry is 20 - 50 wt.%, the addition amount of the anionic dispersant of the additive powder is 0.1 - 1 wt.% of the additive, and it is ground in a sand mill until the particle size of the mixed slurry is 400 - 600 nm; the addition amount of the anionic dispersant of the total slurry is 0.1 - 1 wt.% of the total mass of the powder, the addition amount of the binder is 0.5 - 1 wt.% of the total mass of the powder, the ball milling time is 20 - 24 h, the binder is polyvinyl alcohol, and the anionic dispersant is an ammonium polyacrylate - type dispersant.

4. The preparation method of a large-current varistor chip according to claim 1, characterized in that In step S4, the water - containing aging is to test the water content of the granulated powder, adjust the water content according to the measurement result, so that the water content of the granulated powder is 1.2 - 2 wt.%.

5. The preparation method of a large-current varistor chip according to claim 1, characterized in that, In step S4, the high - temperature sintering step is to heat it up to 800 - 900 °C at a heating rate of 1.5 - 2.0 °C / min, and then heat it up to 1000 - 1200 °C at a heating rate of 0.5 - 1.0 °C / min, keep it warm for 1.5 - 2.5 h and then cool it down with the furnace; the heat treatment temperature is 400 - 600 °C and keep it warm for 1 - 2 h.

6. The preparation method of a large-current varistor chip according to claim 1, characterized in that, The preparation method of the silane coupling agent with a quaternary ammonium fluoride structure is as follows: Disperse 1 eq of ammonium salt silane coupling agent and at least 5 eq of potassium fluoride in methanol, stir at 20 - 30 °C for 40 - 80 min, filter to remove the solid, after rotary evaporation to remove most of the solvent, add dichloromethane, wash the organic phase with deionized water, and remove the solvent to obtain a silane coupling agent with a quaternary ammonium fluoride structure; The ammonium salt silane coupling agent is one or more of 3-triethoxysilylpropyltrimethylammonium chloride, 3-triethoxysilylpropyltrimethylammonium bromide, 3-triethoxysilylpropyltriethylammonium chloride, 3-triethoxysilylpropyltriethylammonium bromide, 3-trimethoxysilylpropyltrimethylammonium chloride, 3-trimethoxysilylpropyltrimethylammonium bromide, 3-trimethoxysilylpropyltriethylammonium chloride, and 3-trimethoxysilylpropyltriethylammonium bromide.

7. A varistor chip with large current-carrying capacity, characterized in that, Obtained by the preparation method of a large current-carrying varistor sheet according to any one of claims 1 - 6.

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