A power capacitor and a method for preparing the same

Abstract

The present invention provides a power capacitor and a preparation method thereof. The raw materials for the preparation of the power capacitor include: positive electrode foil, negative electrode foil, electrolytic paper, positive and negative guide pins, colloid, aluminum shell, casing, and electrolyte. The preparation method of the power capacitor includes the following steps: cutting the positive electrode foil and the negative electrode foil and riveting them with the positive guide pin and the negative guide pin; placing the electrolytic paper between the riveted positive electrode foil and the negative electrode foil and winding them to form a core package, injecting electrolyte into the core package, sealing it in an aluminum shell with colloid and performing mechanized waisting and sealing to obtain a semi-finished capacitor; cleaning the semi-finished capacitor and casing it, aging and selecting, secondary aging and selecting, observing the appearance, and inspecting it in sequence to obtain it. The power capacitor prepared by the present invention not only has a large capacity, but also has good high and low temperature characteristics, strong vibration resistance, voltage shock resistance, and a long life.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum electrolytic capacitors, and in particular relates to a power capacitor and a preparation method thereof. Background Art

[0002] Capacitors play an important role in today's electronic products. Aluminum electrolytic capacitors play an important role in the field of electronic equipment due to their high capacitance, strong current handling capability, compact size, long service life, cost-effectiveness and wide applicability. They are widely used in important fields such as power reserve of household appliances, mid-to-high-end power supplies, hybrid power devices and electric motors, power factor correction, and stability of power transmission and distribution systems. They also play the role of filtering, bypassing, coupling and decoupling in circuits and help improve the efficiency and stability of industrial equipment, reduce energy consumption and costs.

[0003] Power capacitors are one of the important electronic components in power systems, used for reactive power compensation, voltage regulation and filtering, and their performance directly affects the stability and efficiency of the power system. Nowadays, domestic power aluminum electrolytic capacitors often have problems such as large capacitance attenuation, internal temperature rise, and insulation performance degradation after long-term operation, affecting the reliability and service life of the entire equipment. However, existing aluminum electrolytic capacitors do not meet the warranty period requirements of the State Grid and cannot fully meet the special operating environment (high temperature and humidity resistance, low temperature resistance, voltage shock resistance, vibration resistance).

[0004] Therefore, to meet the needs of smart meters and other power grid equipment in extremely low temperature conditions, capacitors must also maintain stable performance to avoid performance degradation or failure due to low temperatures. Therefore, a new type of aluminum electrolytic capacitor is needed. This power capacitor features a simple production process, moderate price, excellent performance at high and low temperatures, resistance to external voltage shocks and vibrations, and easy installation. Summary of the Invention

[0005] The purpose of the present invention is to provide a power capacitor and a method for preparing the same. By optimizing the structure of the capacitor and the preparation process of each component and utilizing a highly reliable product enabling method, the capacitance of the power capacitor is increased, its loss is reduced, and its impact resistance is enhanced, thereby extending the service life of the capacitor and improving the longevity of power grid equipment.

[0006] A power capacitor, the raw materials for its preparation include: positive electrode foil, negative electrode foil, electrolytic paper, positive and negative guide pins, colloid particles, aluminum shell, sleeve, and electrolyte.

[0007] The positive electrode foil and the negative electrode foil are both finished aluminum foils, and their preparation method includes the following steps: boiling the aluminum foil material in high-purity water for 3 to 5 minutes, placing it in a chemical conversion liquid with a temperature of 85 to 90°C for chemical conversion, cleaning it with deionized water after chemical conversion, placing it in a muffle furnace for heat treatment, and then performing secondary chemical conversion to obtain the finished product.

[0008] Preferably, the aluminum foil material can be selected from microporous aluminum foil.

[0009] Preferably, the raw materials for preparing the chemical conversion liquid include high-purity water, boric acid, ammonium pentaborate, borax, and ammonia water.

[0010] In the chemical conversion liquid, the mass fraction of boric acid is 8% to 12%, the mass fraction of ammonium pentaborate is 0.05% to 0.1%, and the mass fraction of borax is 0.01% to 0.05%.

[0011] Preferably, the resistivity of the high-purity water is 15 to 20 MΩ·cm.

[0012] Preferably, the volume concentration of the ammonia water is 20% to 25%.

[0013] The preparation method of the chemical conversion liquid comprises the following steps: dissolving boric acid, ammonium pentaborate and borax in high-purity water in sequence, adding ammonia water to adjust the pH to 5.5-6.5, and stirring evenly to obtain the chemical conversion liquid.

[0014] The inventors have found that the use of a specific boric acid system chemical liquid can not only increase the life of the capacitor, but also improve the high-temperature stability of the capacitor. This may be because, on the one hand, high-purity water is used as a solvent to remove impurities that may interfere with the reaction, improve the purity of the reaction system, and help reduce unnecessary side reactions and additional heat generation; on the other hand, boron-containing compounds such as boric acid, ammonium pentaborate, and borax react relatively mildly in the chemical liquid, generate little heat, and will not produce a violent exothermic reaction, which can reduce the internal temperature rise during use, thereby improving the life and thermal stability of the capacitor. The use of ammonia water to adjust the pH value is not only conducive to the formation of aluminum oxide, but also avoids the violent reaction and heat release caused by excessive acid or alkalinity. In addition, the synergistic effect between the various raw materials of the specific boric acid system chemical liquid can improve the density and stability of the oxide film on the surface of the aluminum foil, thereby improving the voltage resistance of the positive and negative foils, and thus improving the life of the capacitor.

[0015] The formation step adopts constant current and constant voltage method, firstly using 0.04~0.06A / cm 2 Use constant current method to convert the current density to 490-510V, and then use constant voltage method to convert it for 8-10 minutes.

[0016] The secondary formation adopts constant current and constant pressure method, firstly with 0.04~0.06A / cm 2Use constant current method to convert the current density to 490-510V, and then use constant voltage method to convert it for 3-5 minutes.

[0017] Preferably, the heat treatment conditions are: temperature of 480-520° C., and holding time of 1-3 minutes.

[0018] The electrolytic paper is a superposition of medium-density electrolytic paper and high-density electrolytic paper.

[0019] The method for preparing medium-density electrolytic paper comprises the following steps: taking bleached kraft softwood pulp, soaking it in deionized water, beating it to a beating degree of 83-87°SR, diluting it with deionized water until the mass concentration of the absolute dry pulp in the system is 1.5-2.5 g / L, making wet paper, pressing and drying the wet paper, and then calendering it to obtain the medium-density electrolytic paper.

[0020] The viscosity of the bleached kraft softwood pulp is 20-25CP, the ash content is ≤0.3%, the average fiber length is 2-2.5mm, and the average fiber roughness is 15-16mg / 100g; further preferably, the viscosity of the bleached kraft softwood pulp is 22CP, the ash content is 0.2%, the average fiber length is 2.29mm, and the average fiber roughness is 15.5mg / 100g.

[0021] In some preferred embodiments, the bleached kraft softwood pulp is purchased from Kellyville, Canada.

[0022] The inventors discovered that using a specific bleached softwood sulfate pulp as a raw material to produce medium-density electrolytic paper can improve the capacitance and impact resistance of capacitors. This is likely because the longer and more stable fibers of this specific bleached softwood sulfate pulp form a more uniform and dense fiber network within the electrolytic paper, which helps increase the surface area of ​​the electrolytic paper. This not only increases the capacitance of the capacitor, but also enhances the mechanical strength of the capacitor through the dense network formed. However, the performance improvement is limited.

[0023] Preferably, the wet paper making basis weight is 24 to 28 g / m 2 .

[0024] Preferably, the calendering treatment conditions are: temperature 62-66°C, pressure 0.15-0.2 kgf / cm 2 .

[0025] Preferably, the thickness of the medium-density electrolytic paper is 30 to 45 kilograms.

[0026] The method for preparing high-density electrolytic paper comprises the following steps: taking bleached kraft softwood pulp, soaking it in deionized water, beating it to a beating degree of 77-82°SR, and diluting it with first deionized water to obtain a first liquid; taking modified cellulose fiber, mixing it with a second deionized water, dispersing it, adding it to the first liquid, homogenizing it for 2-4 hours, making wet paper, pressing and drying the wet paper, and then calendering it to obtain the high-density electrolytic paper.

[0027] Preferably, the mass concentration of the absolute dry pulp in the liquid 1 is 1.5 to 2.5 g / L.

[0028] Preferably, the added amount of the modified cellulose fiber is 1% to 3% of the mass of the absolute dry pulp.

[0029] Preferably, the mass ratio of the modified cellulose fiber to the second deionized water is 1:(100-200); more preferably, it is 1:150.

[0030] The preparation method of the modified cellulose fiber comprises the following steps: uniformly dispersing the cellulose fiber in a third deionized water, adding a modifier, adjusting the pH of the system to be stable between 10 and 10.5, reacting for 3 to 5 hours, washing the product with deionized water to neutrality, and drying the product.

[0031] Preferably, the cellulose fibers include first cellulose fibers, second cellulose fibers and third cellulose fibers.

[0032] Preferably, the first cellulose fibers have a length of 100 to 1000 μm and a diameter of 100 to 1000 nm.

[0033] Preferably, the second cellulose fibers have a length of 1 to 20 μm and a diameter of 20 to 80 nm.

[0034] Preferably, the third cellulose fibers have a length of 200 to 800 nm and a diameter of 1 to 10 nm.

[0035] In some preferred embodiments, the first cellulose fiber, the second cellulose fiber and the third cellulose fiber are all purchased from MFC, CNF-H1 and CNC produced by Zhejiang Jinjiahao Green Nanomaterials Co., Ltd.

[0036] Preferably, the mass ratio of the first cellulose fibers, the second cellulose fibers and the third nanocellulose is 1:(1-3):(2-4); more preferably, it is 1:2:3.

[0037] Preferably, the mass ratio of the cellulose fiber to the third deionized water is 1:(150-250); more preferably, it is 1:200.

[0038] The inventors discovered that high-density electrolytic paper prepared by adding three different cellulose fibers to a specific bleached sulfate softwood pulp can further improve the capacitance, mechanical strength and stability of the capacitor. This may be because the introduction of three cellulose fibers with different aspect ratios can increase the complexity and diversity of the fiber structure inside the electrolytic paper. The long fibers can provide good conductive channels, promoting the rapid transmission of charge within the electrolytic paper; the short fibers can fill the gaps between the long fibers, forming a tighter fiber network, and improving the density and strength of the electrolytic paper. The synergistic effect of this long and short fibers enables the electrolytic paper to maintain high capacity while also having good stability and durability. During the mixing process, the fibers of the bleached sulfate softwood pulp and the three cellulose fibers with different aspect ratios will interact, helping to strengthen the bonding force between the fibers, so that the high-density electrolytic paper is not easily deformed or broken when subjected to external forces or temperature changes, thereby maintaining stable capacitance performance. At the same time, this bonding force also helps to improve the overall mechanical strength and service life of the electrolytic paper. However, the cellulose fibers have a relatively large aspect ratio and poor dispersion in the bleached sulfate softwood pulp, which affects the performance of the prepared high-density electrolytic paper.

[0039] Preferably, the modifier is 2,2,6,6-tetramethylpiperidinyl oxide, sodium bromide and sodium hypochlorite.

[0040] Preferably, the mass ratio of the 2,2,6,6-tetramethylpiperidinyl oxide, sodium bromide and sodium hypochlorite is 1:(4-6):(290-310); more preferably, it is 1:10:300.

[0041] Preferably, the amount of the modifier added is 5 to 8 times the mass of the cellulose fiber.

[0042] The inventors have discovered that the use of a specific modifier to modify the cellulose fibers and the use of high-speed homogenous dispersion can improve the dispersibility of the cellulose fibers in the bleached sulfate softwood pulp slurry. This may be because 2,2,6,6-tetramethylpiperidinyl oxide and sodium bromide catalyze the selective oxidation of cellulose fibers with sodium hypochlorite. On the one hand, it can destroy the hydrogen bond network of the cellulose fibers in the amorphous region, increase the hydrophilicity and reactivity of the cellulose fibers, and not only help the cellulose fibers to better combine with other components in the subsequent processing process, but also help to improve the overall mechanical strength and service life of the electrolytic paper. It also helps to improve the absorption and retention capacity of the electrolytic paper for the electrolyte, further improving the capacitance performance. On the other hand, the modification also changes the surface structure and chemical properties of the cellulose fibers, thereby increasing the negative charge of the cellulose fibers, helping to disperse and stabilize the cellulose fibers in the slurry, reducing the agglomeration and precipitation of the cellulose fibers, and thus improving the stability and durability of the electrolytic paper.

[0043] Preferably, the wet paper making basis weight is 24 to 28 g / m 2 .

[0044] Preferably, the rotation speed of the high-speed homogenizer is 15000-20000 rpm.

[0045] Preferably, the calendering treatment conditions are: temperature 62-66°C, pressure 0.15-0.2 kgf / cm 2 .

[0046] Preferably, the thickness of the high-density electrolytic paper is 15 to 30 cm.

[0047] Preferably, the electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and an organic solvent.

[0048] Preferably, the concentration of the lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 0.5 to 1.5 mol / L.

[0049] Preferably, the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate, propylene carbonate and N-methylpyrrolidone.

[0050] Preferably, the volume ratio of ethylene carbonate, dimethyl carbonate, propylene carbonate and N-methylpyrrolidone is (1-3):(1-3):(1-3):1; more preferably, it is 2:2:2:1.

[0051] The inventors have found that selecting specific organic solvents and lithium salts to prepare electrolytes can improve the high-temperature and low-temperature resistance of capacitors. This may be because there is a synergistic effect between the four organic solvents. There is good mutual solubility and synergistic effect between ethylene carbonate and propylene carbonate. The addition of ethylene carbonate can reduce the melting point of propylene carbonate and improve the low-temperature performance of the electrolyte. At the same time, the mixing of the two can form a stable solvation structure, which helps the transmission and storage of ions. The use of N-methyl pyrrolidone in combination with ethylene carbonate and propylene carbonate can improve the stability of the electrolyte, promote the efficient transmission of ions, and improve the electrochemical stability of the capacitor. Dimethyl carbonate and propylene carbonate are compounded, which can not only reduce the viscosity of the electrolyte and improve ion mobility, but also reduce the melting point and help improve the low-temperature performance of the electrolyte. In addition, the four organic solvents can improve the wettability of the electrode surface, promote the rapid transmission of ions at the electrode / electrolyte interface, thereby improving capacitance performance.

[0052] The method for preparing a power capacitor comprises the following steps: cutting a positive electrode foil and a negative electrode foil and riveting them with a positive guide pin and a negative guide pin; placing electrolytic paper between the riveted positive electrode foil and the negative electrode foil, winding the paper to form a core package, injecting electrolyte into the core package, sealing the core package in an aluminum shell using colloid particles, and mechanically waisting and sealing the shell to obtain a semi-finished capacitor; and cleaning the semi-finished capacitor, sleeve-fitting the semi-finished capacitor, and sequentially aging and selecting, secondary aging and selecting, observing the appearance, and inspecting the semi-finished capacitor to obtain the capacitor.

[0053] Preferably, the number of layers of the electrolytic paper is 4 (medium-density electrolytic paper and high-density electrolytic paper are stacked into one layer).

[0054] Although high-density electrolytic paper has excellent performance, its processing method is more complicated and has higher cost. The inventor finds that, select medium-density electrolytic paper and high-density electrolytic paper to be superimposed as electrolytic paper, when assembling capacitor, when the number of plies of electrolytic paper is 4 layers, not only can cost be saved, ESR value (equivalent series resistance) can also be reduced, and high voltage impulse force can be promoted simultaneously. This may be because when medium and high-density electrolytic paper are mixed with four layers, on the one hand the electrolytic paper of different densities has different liquid absorption performance and liquid retention capacity, high-density electrolytic paper has better liquid retention capacity usually, and low-density electrolytic paper then has better liquid absorption speed, and this combination can optimize the distribution and maintenance of electrolyte, reduces the loss and volatilization of electrolyte, thereby reduces ESR value. On the other hand multi-layer composite structure can improve the overall fiber structure of electrolytic paper, makes it more uniform and dense, contributes to reducing pore and defect inside electrolytic paper, improves the transmission efficiency of electrolyte, while further reducing ESR value, can also strengthen the withstand voltage capability of whole electrolytic paper structure, improve the impulse force of product under high voltage.

[0055] The conditions for the aging selection and secondary aging selection are: ambient temperature of 155°C, applied voltage of 500V, and continuous application for 12 hours. During this process, the change rate of the leakage recovery value of the capacitor is continuously monitored. If the change rate is ≤10%, the next step can be entered.

[0056] In some preferred solutions, the semi-finished capacitor is subjected to a secondary waisting and then casing after cleaning, which can further improve the stability of the core package in the aluminum shell, prevent the internal structure from changing during use, and improve the vibration resistance of the product.

[0057] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0058] 1. The present invention provides a power capacitor which not only has a large capacity but also has good high and low temperature characteristics, strong vibration resistance, voltage shock resistance, and a long life.

[0059] 2. The present invention uses a boric acid system with low calorific value to form aluminum foil, which reduces the internal temperature rise of the product during use, thereby not only prolonging the life of the capacitor, but also improving the high temperature stability of the capacitor.

[0060] 3. The present invention adopts an electrolyte with low water content and high conductivity, which can improve the high and low temperature resistance of the product.

[0061] 4. The present invention adopts high-purity guide pins and high-voltage aluminum stems to ensure the stability of product parameters and performance.

[0062] 5. The present invention adopts 4 layers of mixed medium and high density electrolytic paper to reduce the ESR value of the product while improving the high voltage impact force.

[0063] 6. The present invention adopts a special aging process to ensure that the leakage current recovery value change rate of the product within the validity period is ≤10%.

[0064] 7. The assembly process of the present invention adopts a double waist method to improve the vibration resistance of the product. DETAILED DESCRIPTION

[0065] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0066] The raw materials used in the present invention are all commercially available, specifically:

[0067] Bleached softwood kraft pulp with a viscosity of 22 cp, ash content of 0.2%, average fiber length of 2.29 mm, and average fiber roughness of 15.5 mg / 100 g was purchased from Kelly, Canada. The first cellulose fiber had a length of 100-1000 μm and a diameter of 100-1000 nm; the second cellulose fiber had a length of 1-20 μm and a diameter of 20-80 nm; and the third cellulose fiber had a length of 200-800 nm and a diameter of 1-10 nm. All were purchased from Zhejiang Jinjiahao Green Nanomaterials Co., Ltd. (MFC, CNF-H1, and CNC). Microporous aluminum foil: Product model MA-EN-CU-0005, CLUDE.

[0068] Example 1

[0069] This embodiment provides a power capacitor, the raw materials for its preparation are: positive electrode foil, negative electrode foil, electrolytic paper, positive and negative guide pins, colloid particles, aluminum shell, casing, and electrolyte.

[0070] The positive electrode foil and the negative electrode foil are both finished aluminum foils, and the preparation method thereof comprises the following steps: boiling the microporous aluminum foil in high-purity water for 4 minutes, placing the foil in a forming solution at a temperature of 88° C. for forming, washing the foil with deionized water after forming, placing the foil in a muffle furnace for heat treatment, and then performing a secondary forming process to obtain the finished product.

[0071] The raw materials for preparing the chemical conversion liquid are high-purity water, boric acid, ammonium pentaborate, borax and ammonia water.

[0072] In the chemical conversion solution, the mass fraction of boric acid is 10%, the mass fraction of ammonium pentaborate is 0.08%, and the mass fraction of borax is 0.03%.

[0073] The resistivity of the high-purity water is 18 MΩ·cm.

[0074] The volume concentration of the ammonia water is 22%.

[0075] The preparation method of the chemical conversion liquid comprises the following steps: dissolving boric acid, ammonium pentaborate and borax in high-purity water in sequence, adding ammonia water to adjust the pH to 6.0, and stirring evenly to obtain the chemical conversion liquid.

[0076] The formation step adopts constant current and constant voltage method, first with 0.05A / cm 2 The current density was set to 500V, and then the constant current method was used for formation. After the voltage reached 500V, the constant voltage method was used for formation for 9 minutes.

[0077] The secondary formation adopts constant current and constant pressure method, first with 0.05A / cm 2 The current density was set to 500V, and then the constant current method was used for formation. After the voltage reached 500V, the constant voltage method was used for formation for 4 minutes.

[0078] The heat treatment conditions are: temperature of 500° C. and holding time of 2 minutes.

[0079] The electrolytic paper is a superposition of medium-density electrolytic paper and high-density electrolytic paper.

[0080] The method for preparing medium-density electrolytic paper comprises the following steps: taking bleached kraft softwood pulp, soaking it in deionized water, beating it to a beating degree of 85°SR, diluting it with deionized water until the mass concentration of the absolute dry pulp in the system is 2.0 g / L, making wet paper, pressing and drying the wet paper, and then calendering it to obtain the medium-density electrolytic paper.

[0081] The wet paper making basis weight is 26 g / m 2 .

[0082] The calendering treatment conditions are: temperature 65°C, pressure 0.18 kgf / cm 2 .

[0083] The thickness of the medium density electrolytic paper is 30 kilograms.

[0084] The method for preparing high-density electrolytic paper comprises the following steps: soaking bleached kraft softwood pulp in deionized water, beating the pulp to a beating degree of 80°SR, and diluting the pulp with first deionized water to obtain a first liquid; dispersing modified cellulose fiber in a second deionized water, adding the dispersed fiber to the first liquid, homogenizing the fiber for 3 hours, making wet paper, pressing and drying the wet paper, and calendering the wet paper to obtain the high-density electrolytic paper.

[0085] The mass concentration of the absolute dry pulp in the liquid 1 is 2.0 g / L.

[0086] The added amount of the modified cellulose fiber is 2% of the mass of the absolute dry pulp.

[0087] The mass ratio of the modified cellulose fiber to the second deionized water is 1:150.

[0088] The preparation method of the modified cellulose fiber comprises the following steps: uniformly dispersing the cellulose fiber in a third deionized water, adding a modifier, adjusting the pH of the system to be stable at about 10.3, reacting for 4 hours, washing the product with deionized water to neutrality, and drying the product.

[0089] The mass ratio of the cellulose fiber to the third deionized water is 1:200.

[0090] The modifiers are 2,2,6,6-tetramethylpiperidinyl oxide, sodium bromide and sodium hypochlorite.

[0091] The mass ratio of the 2,2,6,6-tetramethylpiperidinium oxide, sodium bromide and sodium hypochlorite is 1:10:300.

[0092] The added amount of the modifier is 6 times the mass of the cellulose fiber.

[0093] The cellulose fibers include first cellulose fibers, second cellulose fibers and third cellulose fibers.

[0094] The mass ratio of the first cellulose fibers, the second cellulose fibers and the third nanocellulose is 1:2:3.

[0095] The wet paper making basis weight is 26 g / m 2 .

[0096] The rotation speed of the high-speed homogenizer is 18000 rpm.

[0097] The calendering treatment conditions are: temperature 65°C, pressure 0.18 kgf / cm 2 .

[0098] The thickness of the high-density electrolytic paper is 30 kilograms.

[0099] The electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide and an organic solvent.

[0100] The concentration of the lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 1.0 mol / L.

[0101] The organic solvent is a mixture of ethylene carbonate, dimethyl carbonate, propylene carbonate and N-methylpyrrolidone.

[0102] The volume ratio of the ethylene carbonate, dimethyl carbonate, propylene carbonate and N-methylpyrrolidone is 2:2:2:1.

[0103] The preparation method of the power capacitor comprises the following steps: cutting the positive electrode foil and the negative electrode foil and riveting them with the positive guide pin and the negative guide pin; placing electrolytic paper between the riveted positive electrode foil and the negative electrode foil, winding them to form a core package, injecting electrolyte into the core package, sealing it in an aluminum shell with colloid particles, and mechanically waisting and sealing it to obtain a semi-finished capacitor; cleaning the semi-finished capacitor, sleeve it, and then subjecting it to aging selection, secondary aging selection, observing its appearance, and inspecting it in sequence to obtain the capacitor.

[0104] The number of layers of the electrolytic paper is 4.

[0105] The conditions for the aging selection and secondary aging selection are: ambient temperature of 155°C, applied voltage of 500V, and continuous application for 12 hours. During this process, the change rate of the leakage recovery value of the capacitor is continuously monitored. If the change rate is ≤10%, the next step can be entered.

[0106] Example 2

[0107] The difference between this embodiment and embodiment 1 is that the thickness of the medium-density electrolytic paper is 40 cm; the thickness of the high-density electrolytic paper is 20 cm; and the semi-finished capacitor is subjected to secondary waisting and then casing after cleaning.

[0108] Example 3

[0109] The difference between this embodiment and embodiment 2 is that in the chemical conversion solution, the mass fraction of boric acid is 10%, the mass fraction of ammonium pentaborate is 0.1%, and the mass fraction of borax is 0.05%.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 2 is that the raw materials for preparing the chemical conversion liquid are high-purity water and phosphoric acid; and the mass fraction of phosphoric acid in the chemical conversion liquid is 10%.

[0112] Comparative Example 2

[0113] The difference between this comparative example and Example 2 is that the raw materials for preparing the chemical conversion liquid are high-purity water and boric acid; and the mass fraction of boric acid in the chemical conversion liquid is 10%.

[0114] Comparative Example 3

[0115] The difference between this comparative example and Example 2 is that the viscosity of the bleached kraft softwood pulp is 20 CP, the average fiber length is 3.1 mm, and the average fiber roughness is 20 mg / 100 g.

[0116] The bleached kraft softwood pulp was purchased from Canada Haosheng, Haosheng 100.

[0117] Comparative Example 4

[0118] The difference between this comparative example and Example 2 is that the electrolytic paper is medium-density electrolytic paper.

[0119] Comparative Example 5

[0120] The difference between this comparative example and Example 2 is that the method for preparing high-density electrolytic paper comprises the following steps: taking bleached kraft softwood pulp, soaking it in deionized water, beating it to a beating degree of 80°SR, and diluting it with a first deionized water to obtain liquid 1; taking cellulose fiber, mixing it in deionized water, and dispersing it, adding it to liquid 1, homogenizing it for 3 hours, making wet paper, pressing and drying the wet paper, and then calendering it to obtain high-density electrolytic paper.

[0121] Comparative Example 6

[0122] The difference between this comparative example and Example 2 is that the cellulose fibers are first cellulose fibers.

[0123] Comparative Example 7

[0124] The difference between this comparative example and Example 2 is that the modifiers are sodium bromide and sodium hypochlorite; and the mass ratio of the sodium bromide to the sodium hypochlorite is 1:30.

[0125] Comparative Example 8

[0126] The difference between this comparative example and Example 2 is that the number of layers of the electrolytic paper is one.

[0127] Comparative Example 9

[0128] The difference between this comparative example and Example 2 is that the electrolyte is lithium bis(trifluoromethanesulfonyl)imide and high-purity water.

[0129] Comparative Example 10

[0130] The difference between this comparative example and Example 2 is that the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate and N-methylpyrrolidone; and the volume ratio of the ethylene carbonate, dimethyl carbonate and N-methylpyrrolidone is 2:2:1.

[0131] Performance Testing

[0132] The positive foil is applied with 600VF and the negative foil is applied with 3V. The capacitance, loss factor DF and leakage current LC of the power capacitor are tested according to the method in GB / T 6346.1-2024 "Fixed capacitors for electronic equipment Part 1: General specification".

[0133] Mechanical shock test: Fix the capacitor to the test equipment, with a pulse time of 6ms and an acceleration of 100g / s half sine wave. Apply 6 times in each direction of 3 mutually perpendicular axes. After recovering for 1 to 2 hours, test the capacitance of the power capacitor. The capacitance loss rate is (initial capacitance - capacitance after test) / initial capacitance × 100%.

[0134] Vibration test: Fix the capacitor to the test equipment, with a peak acceleration of 5g / s; 4 cycles in each of three directions, with a frequency from 10Hz to 2000Hz, each cycle time of 20min, for a total test of 12h. After 1-2 hours of recovery, test the capacitance of the power capacitor and calculate the capacitance loss rate.

[0135] High-temperature resistance test: The capacitors were stored at 110°C and 450V for 10,000 hours. After 1-2 hours of recovery, the capacitance of the power capacitors was measured and the capacitance loss rate was calculated. The results are shown in Table 1.

[0136] Table 1 Measurement results

[0137]

[0138]

[0139] According to statistics, the power capacitors prepared by Examples 1 to 3 of the present invention not only have good capacitance characteristics and large capacitance, but also have strong vibration resistance, voltage shock resistance, good high temperature characteristics, and long service life. Comparative Example 1 uses phosphoric acid as the chemical conversion liquid, Comparative Example 2 does not add ammonium pentaborate, borax, or ammonia water to the chemical conversion liquid, Comparative Example 3 has relatively large fiber average length and roughness, Comparative Example 4 does not add medium density electrolytic paper, Comparative Example 5 does not modify the cellulose fiber, Comparative Example 6 does not add the second cellulose fiber and the third cellulose fiber, Comparative Example 7 does not add 2,2,6,6-tetramethylpiperidinoxide, Comparative Example 8 has too few electrolytic paper layers, Comparative Example 9 has water as the electrolyte, and Comparative Example 10 does not contain propylene carbonate in the organic solvent. The power capacitors prepared have defects. Therefore, the power capacitors prepared by the raw materials and methods described in this application not only have large capacity, but also have good high and low temperature characteristics, strong vibration resistance, voltage shock resistance, and long service life.

[0140] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A power capacitor, characterized in that: The raw materials for its preparation include: positive electrode foil, negative electrode foil, electrolytic paper, positive and negative guide pins, colloid particles, aluminum shell, casing, and electrolyte; The positive electrode foil and the negative electrode foil are both finished aluminum foils, and the preparation method thereof comprises: boiling the aluminum foil material in high-purity water for 3 to 5 minutes, placing it in a forming solution at a temperature of 85 to 90° C. for forming, washing it with deionized water after forming, placing it in a muffle furnace for heat treatment, and then performing a secondary forming to obtain the aluminum foil; The raw materials for preparing the chemical conversion liquid include high-purity water, boric acid, ammonium pentaborate, borax, and ammonia water; In the chemical conversion solution, the mass fraction of boric acid is 8% to 12%, the mass fraction of ammonium pentaborate is 0.05% to 0.1%, and the mass fraction of borax is 0.01% to 0.05%; The electrolytic paper is a superposition of medium-density electrolytic paper and high-density electrolytic paper; The method for preparing medium-density electrolytic paper comprises: soaking bleached softwood sulfate pulp in deionized water, beating the pulp to a beating degree of 83-87°SR, diluting the pulp with deionized water to a mass concentration of 1.5-2.5 g / L of absolute dry pulp, making wet paper, pressing and drying the wet paper, and then calendering the wet paper to obtain the medium-density electrolytic paper; The bleached kraft softwood pulp has a viscosity of 20-25 CP, an ash content of ≤0.3%, an average fiber length of 2-2.5 mm, and an average fiber roughness of 15-16 mg / 100 g; The method for preparing high-density electrolytic paper comprises: soaking bleached softwood sulfate pulp in deionized water, beating the pulp to a beating degree of 77-82°SR, and diluting the pulp with first deionized water to obtain a first liquid; dispersing modified cellulose fiber in a second deionized water, adding the dispersed fiber to the first liquid, homogenizing the fiber for 2-4 hours, making wet paper, pressing and drying the wet paper, and calendering the wet paper to obtain the high-density electrolytic paper; The preparation method of the modified cellulose fiber comprises the following steps: uniformly dispersing the cellulose fiber in a third deionized water, adding a modifier, adjusting the pH of the system to be stable between 10 and 10.5, reacting for 3 to 5 hours, washing the product with deionized water until it is neutral, and drying the product; The cellulose fibers include cellulose fibers having different aspect ratios: first cellulose fibers, second cellulose fibers, and third cellulose fibers.

2. The power capacitor according to claim 1, characterized in that: The resistivity of the high-purity water is 15-20 MΩ·cm.

3. A method for preparing a power capacitor according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: cutting the positive electrode foil and the negative electrode foil and riveting them with the positive guide pin and the negative guide pin; placing electrolytic paper between the riveted positive electrode foil and the negative electrode foil, winding them to form a core package, injecting electrolyte into the core package, sealing it in an aluminum shell with colloid particles, and mechanically waisting and sealing it to obtain a semi-finished capacitor; cleaning the semi-finished capacitor, sleeve it, and subjecting it to aging selection, secondary aging selection, appearance observation, and inspection in sequence to obtain the capacitor.

4. The method for preparing a power capacitor according to claim 3, wherein: The number of layers of the electrolytic paper is 4.

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