Long-chain hydroxyl-containing branched dicarboxylic acids, their preparation methods and applications

Abstract

This invention relates to the field of electrolyte technology for aluminum electrolytic capacitors, and discloses a long-chain hydroxyl-containing branched dicarboxylic acid, its preparation method, and its applications. The preparation method of the long-chain hydroxyl-containing branched dicarboxylic acid includes: under the action of an oxidant and an acid, the dimer acid represented by formula (II) undergoes a sequential olefin bond epoxidation reaction and a ring-opening hydrolysis reaction; wherein n is an integer from 1 to 10, and m is an integer from 5 to 15. The synthesized long-chain hydroxyl-containing branched dicarboxylic acid contains multiple hydroxyl groups, has a long carbon chain, and exhibits good comprehensive properties such as good solubility, high flash voltage, and good heat resistance.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology for aluminum electrolytic capacitors, specifically to a long-chain hydroxyl-containing branched dicarboxylic acid, its preparation method, and its application. Background Technology

[0002] Aluminum electrolytic capacitors are mainly composed of alumina electrode foil, electrolyte, and separator. The electrolyte plays a crucial role in capacitor performance, determining its operating temperature range, rated voltage, losses, impedance, ripple current, and service life. The electrolyte for aluminum electrolytic capacitors mainly consists of three parts: solvent, solute, and additives. The solvent is the carrier for dissolving the solute and additives, accounting for 70-90 wt% of the electrolyte composition, primarily composed of systems such as ethylene glycol, glycerol, and γ-butyrolactone. The solute is the core component of the electrolyte, playing a key role in repairing defects in the anode foil oxide film and improving the electrolyte conductivity; it is mainly composed of straight-chain or branched ammonium carboxylate salts. Additives are property modifiers of the electrolyte, mainly including flash voltage enhancers, corrosion inhibitors, hydrogen scavengers, and stabilizers.

[0003] Currently, the main solutes in the electrolytes of aluminum electrolytic capacitors are straight-chain or branched ammonium carboxylate salts, including ammonium succinate, ammonium 2-ethyl-adipate, ammonium 2-butyloctanoate, ammonium azelaate, and ammonium 2-methylazelaate-borate. Branched ammonium carboxylate salts exhibit significantly better solubility, stability, flash voltage, and service life than straight-chain carboxylate salts, making them a third-generation organic aluminum capacitor electrolyte solute and representing the mainstream direction of current aluminum capacitor electrolyte development and a research hotspot. For example, patent application CN1602532A discloses a method for preparing α-branched dicarboxylic acids using malonic acid ester as a starting material, sequentially reacting with monohaloalkanes and dihaloalkanes through substitution, saponification, and high-temperature decarboxylation reactions. The resulting electrolyte exhibits a conductivity of approximately 2 mS / cm and a flash voltage between 450 and 540 V. Patent application CN115116751A discloses a method using diphenylmethylene cyclohexanone and hydroxyketoglutarate as raw materials, undergoing an addition reaction under the action of methylthiazole bromide and a phase transfer catalyst to obtain a dihydroxycarboxylic acid. This carboxylic acid is then converted into an ammonium salt and used to prepare an electrolyte with a flash voltage between 480 and 495 V and a conductivity of approximately 2.2 mS / cm. Patent application CN114380684A discloses a method using cyclohexanedione and methanol as raw materials, undergoing a ring-opening reaction to prepare branched carboxylic acids, followed by esterification of straight-chain carboxylic acids, saponification of branched carboxylic acids, and acidification of branched carboxylate salts to obtain a carbonyl-containing branched carboxylic acid. This is then formulated into an ethylene glycol-based electrolyte with a conductivity of 1.24 mS / cm and an impedance of 857.4 Ω·cm, but its flash voltage was not measured. Patent application JP2007126611A discloses a method using castor oil ester as a raw material, selectively oxidizing the hydroxyl groups with PCC to obtain castor oil ketoester, then converting it to castor oil dicarboxylate via an HWE (Horner-Wadsworth-Emmons) reaction, and further obtaining a branched long-chain dicarboxylic acid through saponification and acid treatment. This dicarboxylate exhibits a conductivity between 1.3 and 1.6 mS / cm in the working electrolyte, a flash voltage above 550V, and good heat resistance. However, these methods for preparing branched dicarboxylic acids suffer from problems such as multi-step reactions, numerous side reactions due to high-temperature decarboxylation, low overall yield, poor solubility of some compounds, low flash voltage of the electrolyte after compounding, and poor heat resistance, making it difficult to meet the needs of the modern high-end capacitor industry. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low flash voltage and poor heat resistance of branched ammonium carboxylate salts in existing technologies, and to provide a long-chain hydroxyl-containing branched dicarboxylic acid, its preparation method, and its applications. The long-chain hydroxyl-containing branched dicarboxylic acid of this invention contains multiple hydroxyl groups, exhibiting good solubility, high flash voltage, and good heat resistance, meeting the requirements of high-end aluminum capacitor applications.

[0005] To achieve the above objectives, the present invention provides a long-chain hydroxyl-containing branched dicarboxylic acid, the structural formula of which is shown in formula (I).

[0006]

[0007] Where n is an integer from 1 to 10, and m is an integer from 5 to 15.

[0008] The second aspect of the present invention provides a method for preparing the above-mentioned long carbon chain hydroxyl-containing branched dicarboxylic acid, the method comprising: subjecting the dimer acid represented by formula (II) to an olefin bond epoxidation reaction and a ring-opening hydrolysis reaction in sequence under the action of an oxidant and an acid;

[0009]

[0010] Where n is an integer from 1 to 10, and m is an integer from 5 to 15.

[0011] Preferably, the molar ratio of the dimer acid to the oxidant is 1:2 to 10.

[0012] Preferably, the oxidant is at least one selected from m-chloroperoxybenzoic acid, tert-butyl hydroperoxide, peracetic acid, hydrogen peroxide, acetic acid / hydrogen peroxide, and sodium hypochlorite.

[0013] Preferably, the solvent for the olefin epoxidation reaction is at least one of dichloromethane, dichloroethane, chloroform, chlorobenzene, and water.

[0014] Preferably, the temperature of the olefin epoxidation reaction is -10℃ to 60℃.

[0015] Preferably, the molar ratio of the acid to the dimer acid is 0.5 to 5:1.

[0016] Preferably, the acid is an organic acid or an inorganic acid.

[0017] Preferably, the organic acid is at least one selected from acetic acid, propionic acid, and trifluoroacetic acid.

[0018] Preferably, the inorganic acid is at least one selected from sulfuric acid, phosphoric acid, and hydrochloric acid.

[0019] Preferably, the solvent for the ring-opening hydrolysis reaction is at least one of methanol, ethanol, methyl tert-butyl ether, and N,N-dimethylformamide.

[0020] Preferably, the temperature of the ring-opening hydrolysis reaction is room temperature to 100°C.

[0021] A third aspect of the present invention provides an electrolyte containing an ammonium salt of the long-chain hydroxyl-branched dicarboxylic acid described in the present invention and a solvent.

[0022] Preferably, in the electrolyte, the concentration of the ammonium salt of the long-chain hydroxyl-branched dicarboxylic acid is 10-30 wt%.

[0023] Preferably, the pH value of the electrolyte is 7-8.

[0024] Preferably, the solvent is at least one of ethylene glycol, glycerol, and γ-butyrolactone.

[0025] A fourth aspect of the present invention provides a method for preparing the electrolyte described above, the method comprising: dissolving the long-chain hydroxyl-containing branched dicarboxylic acid in the solvent, and then introducing ammonia gas.

[0026] The fifth aspect of the present invention provides the application of the electrolyte described above in aluminum electrolytic capacitors.

[0027] Through the above technical solution, this invention uses bio-based dimer acids as raw materials to synthesize the target product, a long-chain hydroxyl-containing branched dicarboxylic acid, in a two-step reaction. The reaction is simple and yields high; the raw materials are widely available, inexpensive, and readily available; the equipment requirements are simple and the synthesis is easy to scale up. The synthesized long-chain hydroxyl-containing branched dicarboxylic acid contains multiple hydroxyl groups, has a long carbon chain, and exhibits good solubility, high flash voltage, and good heat resistance, among other comprehensive properties. Attached Figure Description

[0028] Figure 1 This is the 1H NMR spectrum of the dicarboxylic acid C32-HDA prepared in Example 1. 1 H-NMR);

[0029] Figure 2 This is the carbon NMR spectrum of the dicarboxylic acid C32-HDA prepared in Example 1. 13 C-NMR);

[0030] Figure 3 The image shows the Fourier transform infrared (FT-IR) spectrum of the dicarboxylic acid C32-HDA prepared in Example 1.

[0031] Figure 4 The image shows the Fourier transform infrared (FT-IR) spectrum of the dicarboxylic acid C36-HDA prepared in Example 2.

[0032] Figure 5 This is the mass spectrum (ESI-MS) of the dicarboxylic acid C32-HDA prepared in Example 1;

[0033] Figure 6 This is the mass spectrum (ESI-MS) of the dicarboxylic acid C36-HDA prepared in Example 2. Detailed Implementation

[0034] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0035] The structural formula of the long carbon chain hydroxyl-containing branched dicarboxylic acid described in this invention is shown in formula (I).

[0036]

[0037] In equation (I), n is an integer from 1 to 10. Specifically, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, preferably 2-5.

[0038] In equation (I), m is an integer from 5 to 15. Specifically, it can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, preferably 6 to 10.

[0039] In a preferred embodiment, the long-chain hydroxyl-containing branched dicarboxylic acid is 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipropylcyclohexyl]-9,10-dihydroxyundecanoic acid and / or 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipentylcyclohexyl]-9,10-dihydroxyundecanoic acid.

[0040] The present invention also provides a method for preparing the above-mentioned long carbon chain branched dicarboxylic acid containing hydroxyl groups, the method comprising: subjecting the dimer acid represented by formula (II) to an olefin bond epoxidation reaction and a ring-opening hydrolysis reaction in sequence under the action of an oxidant and an acid;

[0041]

[0042] The definitions of n and m are the same as those described above.

[0043] According to the method described in this invention, using the dimer acid as a raw material, a olefin bond epoxidation reaction and a ring-opening hydrolysis reaction are carried out sequentially to obtain the long-chain hydroxyl-containing branched dicarboxylic acid described in this invention. The specific reaction process is shown in the following formula.

[0044]

[0045] In the method described in this invention, the molar ratio of the dimer acid to the oxidant can be 1:2 to 10, preferably 1:2 to 5, and most preferably 1:3.

[0046] In the method described in this invention, the dimer acid may be derived from vegetable oleic acid or obtained by the addition of vegetable oleic acid with other long-chain unsaturated carboxylic acids. As a specific example, the dimer acid includes dimeroctadecenoic acid (i.e., 11-(2-(8-carboxyoctyl)-5,6-dipentylcyclohex-3-en-1-yl)undecenoic acid, where m = 7 and n = 4 in formula (II), dimerhexadecenoic acid (i.e., 11-(2-(8-carboxyoctyl)-5,6-dipropylcyclohex-3-en-1-yl)undecenoic acid, where m = 7 and n = 2 in formula (II), etc.

[0047] In the method described in this invention, the oxidant may be at least one selected from m-chloroperoxybenzoic acid, tert-butyl hydroperoxide, peracetic acid, hydrogen peroxide, acetic acid / hydrogen peroxide, and sodium hypochlorite. In a preferred embodiment, the oxidant is acetic acid / hydrogen peroxide.

[0048] In the method described in this invention, the reaction system for the olefin epoxidation reaction may or may not contain a solvent. The solvent used in the olefin epoxidation reaction may be at least one of dichloromethane, dichloroethane, chloroform, chlorobenzene, and water, preferably dichloromethane and / or water.

[0049] In the method described in this invention, the temperature of the olefin epoxidation reaction can be -10℃ to 60℃, preferably -5℃ to room temperature.

[0050] In the method described in this invention, the molar ratio of the acid to the dimer acid can be 0.5 to 5:1, preferably 0.8 to 2:1, and most preferably 1:1.

[0051] In the method described in this invention, the acid can be an organic acid or an inorganic acid. For example, the organic acid can be at least one of acetic acid, propionic acid, and trifluoroacetic acid; the inorganic acid can be at least one of sulfuric acid, phosphoric acid, and hydrochloric acid.

[0052] In the method described in this invention, the reaction system of the ring-opening hydrolysis reaction may or may not contain a solvent. The solvent used in the ring-opening hydrolysis reaction may be at least one selected from methanol, ethanol, methyl tert-butyl ether, and N,N-dimethylformamide, preferably ethanol.

[0053] In the method described in this invention, the temperature of the ring-opening hydrolysis reaction can be from room temperature to 100°C, with the most preferred temperature being 60°C.

[0054] The method described in this invention also includes a separation and purification step. Specifically, after the reaction is completed, an appropriate amount of water and ethyl acetate are added to the reaction system, the mixture is separated, washed, and the organic phase is retained. The organic phase is dried, filtered, and the solvent is removed by distillation to obtain the target product.

[0055] The present invention also provides an electrolyte containing an ammonium salt of the long-chain hydroxyl-branched dicarboxylic acid described in the present invention and a solvent.

[0056] In the electrolyte, the concentration of the ammonium salt of the long-chain hydroxyl-branched dicarboxylic acid can be 10-30 wt%, preferably 10 wt%. The pH value of the electrolyte can be 7-8, most preferably 7.5.

[0057] In the electrolyte, the solvent can be a commonly used electrolyte solvent in the art. For example, the solvent can be at least one of ethylene glycol, glycerol, and γ-butyrolactone.

[0058] The present invention also provides a method for preparing the electrolyte described above, the method comprising: dissolving the long-chain hydroxyl-containing branched dicarboxylic acid in the solvent, and then introducing ammonia gas.

[0059] In some embodiments, the preparation method of the electrolyte includes: dissolving the long-chain hydroxyl-containing branched dicarboxylic acid in ethylene glycol, then introducing ammonia gas into the prepared ethylene glycol solution to adjust the pH value of the ethylene glycol solution to about 7.5, thereby obtaining the electrolyte.

[0060] This invention also provides the application of the electrolyte described above in aluminum electrolytic capacitors. In practical applications, the electrolyte exhibits good solubility, high flash voltage, and good heat resistance without the addition of any additives, thus meeting the application requirements of high-end aluminum capacitors.

[0061] The following examples further illustrate the long-chain hydroxyl-containing branched dicarboxylic acids, their preparation methods, and applications according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0062] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0063] In the following examples, 11-(2-(8-carboxyoctyl)-5,6-dipropylcyclohex-3-en-1-yl)undecenoic acid (C 32 H 56 O4) and 11-(2-(8-carboxyoctyl)-5,6-dipentylcyclohex-3-en-1-yl)undecenoic acid (C 36 H 64 All O4 was purchased from Shanghai Titan Technology Co., Ltd.

[0064] Example 1

[0065] Synthesis of 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipropylcyclohexyl]-9,10-dihydroxyundecanoic acid (C32-HDA)

[0066] In a 250 mL round-bottom flask, 50.5 g (100.0 mmol) of 11-(2-(8-carboxyoctyl)-5,6-dipropylcyclohex-3-en-1-yl)undecenoic acid, 6.0 g (100.0 mmol) of acetic acid, and 0.5 mL of concentrated sulfuric acid were added. The mixture was stirred and heated to 40 °C. Hydrogen peroxide (34.0 g, 300.0 mmol) was slowly added dropwise. After the addition was complete, the temperature was slowly increased to 60 °C and the reaction was continued for 6 h. The reaction endpoint was monitored by TLC. Then, an appropriate amount of ethyl acetate was added to dissolve the reaction mixture. The mixture was washed three times with water, and the organic phase was retained and dried over anhydrous Na2SO4. After filtration, the mixture was evaporated to dryness to obtain the target product 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipropylcyclohexyl]-9,10-dihydroxyundecanoic acid (C32-HDA).

[0067] C32-HDA: 3.33 g of orange-yellow transparent viscous liquid, yield 97%. 1 H NMR (400MHz, CDCl3) 5.30 (s, 4H), δ2.35 (p, J = 7.4Hz, 6H), 2.10 (t, 4H)), 1.62 (d, J = 7.2Hz, 4H), 1.40–1.21 (m, 36H), 0.88 (t, J = 5.9Hz, 6H). 13 C NMR(101MHz, CDCl3)δ176.92(s),81.15(s),53.44(s),,33.99(s),31.86(s),29.70(s) ),29.02(s),26.73(s),25.05(s),24.60(s),22.67(s),20.77(s),14.11(s).ESI-MS(M + )cal.for[C 32 H 58 O8 2+ ]285.21, found 258.22.

[0068] The 1H NMR spectrum of C32-HDA, a dicarboxylic acid (C32-HDA) 1 H-NMR, carbon NMR spectrum ( 13 C-NMR, FT-IR, and ESI-MS spectra are shown below. Figure 1 , 2 As shown in Figures 3 and 5.

[0069] Example 2

[0070] Synthesis of 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipentylcyclohexyl]-9,10-dihydroxyundecanoic acid (C36-HDA)

[0071] In a 250 mL round-bottom flask, 56.1 g (100.0 mmol) of 11-(2-(8-carboxyoctyl)-5,6-dipentylcyclohex-3-en-1-yl)undecenoic acid, 6.0 g (100.0 mmol) of acetic acid, and 0.5 mL of concentrated sulfuric acid were added. The mixture was stirred and heated to 40 °C. Hydrogen peroxide (34.0 g, 300.0 mmol) was slowly added dropwise. After the addition was complete, the temperature was slowly increased to 60 °C and the reaction was continued for 6 h. An appropriate amount of ethyl acetate was added to dissolve the reaction mixture. The mixture was washed three times with water, and the organic phase was retained and dried over anhydrous Na2SO4. After filtration, the mixture was evaporated to dryness to obtain the target product, 11-(2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipentylcyclohexyl)-9,10-dihydroxyundecanoic acid (C36-HDA).

[0072] C36-HDA: 5.13 g of yellow, transparent, viscous liquid, yield 91%. 1 H NMR (400MHz, CDCl3) δ5.30 (s, 4H), 2.63–2.43 (m, 4H), 2.35 (p, J = 7.5Hz, 6H), 1.63 (t, J = 7.2Hz, 4H), 1.46–1.08 (m, 44H), 0.96–0.79 (t, 6H). 13 C NMR(101MHz, CDCl3)δ179.84(s),69.62(s),53.43(s),34.01(s),31.94(s),29. 34(s),28.95(s),25.01(s),24.67(s),23.57(s),22.70(s),14.13(s).ESI-MS(M + )cal.for[C 36 H 66 O8 2+ ]313.24, found 313.24.

[0073] The infrared spectrum (FT-IR) and mass spectrum (ESI-MS) of the dicarboxylic acid C36-HDA are shown below. Figure 4 and 6 As shown.

[0074] Example 3

[0075] Preparation of electrolyte

[0076] The dicarboxylic acid C32-HDA was further purified to remove ions, and ethylene glycol was added to prepare a 10 wt% ethylene glycol solution. Ammonia gas was then introduced for ammoniation, and the endpoint was monitored until the pH of the solution reached approximately 7.5, thus obtaining the ammonium carboxylic acid salt electrolyte C32-HDA-NH4. + .

[0077] Example 4

[0078] Preparation of electrolyte

[0079] The dicarboxylic acid C36-HDA was further purified to remove ions, and ethylene glycol was added to prepare a 10 wt% ethylene glycol solution. Ammonia gas was then introduced for ammoniation, and the endpoint was monitored until the pH of the solution reached approximately 7.5, thus obtaining the ammonium carboxylic acid salt electrolyte C36-HDA-NH4. + .

[0080] Test case

[0081] (1) Flash voltage of electrolyte

[0082] Without adding any other additives, the ammonium carboxylate electrolytes prepared in Examples 3 and 4 were used as working electrolytes for aluminum electrolytic capacitors. The relevant properties of each working electrolyte were tested and compared with those of electrolytes prepared with existing diammonium salts. The results are shown in Table 1.

[0083] Table 1: Performance List of Working Electrolytes for Synthetic Carboxylic Acids

[0084] electrolyte pH value Moisture content (wt%) Flashover voltage (V) <![CDATA[Example 3: C32-HDA-NH4 + > 7.47 0.18 532 <![CDATA[Example 4: C36-HDA-NH4 + > 7.51 0.16 526 Ammonium sebacate 7.42 0.12 427 2-Ethylhexanoic acid ammonium 7.39 0.17 442

[0085] As can be seen from the data in Table 1, when the solute prepared by the long carbon chain hydroxyl-containing branched dicarboxylic acid of the present invention is used as the electrolyte, its flash voltage is significantly improved compared with the existing representative straight-chain ammonium carboxylate and branched ammonium carboxylate, with an improvement of about 70 to 90 V.

[0086] (2) Temperature resistance of the electrolyte

[0087] The ammonium carboxylate electrolyte prepared above was kept at 105℃ and its conductivity was measured for different durations. The results are shown in Table 2.

[0088] Table 2: Changes in conductivity of electrolyte at different durations under constant temperature of 105℃

[0089]

[0090] As can be seen from the data in Table 2, when the solute prepared by the long carbon chain hydroxyl-containing branched dicarboxylic acid of the present invention is used as the electrolyte, its temperature resistance is significantly improved compared with the existing representative straight-chain ammonium carboxylate and branched ammonium carboxylate, with an improvement of about 50%.

[0091] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A long-chain, hydroxyl-branched dicarboxylic acid, characterized in that, The long-chain hydroxyl-containing branched dicarboxylic acid is 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipropylcyclohexyl]-9,10-dihydroxyundecanoic acid or 11-[2-(8-carboxyoctyl)-3,4-dihydroxy-5,6-dipentylcyclohexyl]-9,10-dihydroxyundecanoic acid.

2. A method for preparing the long-chain, hydroxyl-containing branched dicarboxylic acid of claim 1, characterized in that, The method includes: subjecting a dimer acid to sequential olefin epoxidation and ring-opening hydrolysis reactions under the action of an oxidant and an acid; The dimer acid is 11-(2-(8-carboxyoctyl)-5,6-dipentylcyclohex-3-en-1-yl)undecenoic acid or 11-(2-(8-carboxyoctyl)-5,6-dipropylcyclohex-3-en-1-yl)undecenoic acid; The oxidant is at least one of m-chloroperoxybenzoic acid, tert-butyl hydroperoxide, peracetic acid, hydrogen peroxide, acetic acid / hydrogen peroxide, and sodium hypochlorite. The acid is an organic acid or an inorganic acid, wherein the organic acid is at least one of acetic acid, propionic acid, and trifluoroacetic acid; and the inorganic acid is at least one of sulfuric acid, phosphoric acid, and hydrochloric acid.

3. The method according to claim 2, characterized in that, The molar ratio of the dimer acid to the oxidant is 1:2~10.

4. The method according to claim 2 or 3, characterized in that, The solvent for the olefin epoxidation reaction is at least one of dichloromethane, dichloroethane, chloroform, chlorobenzene, and water; and / or The epoxidation reaction of the olefin bond is carried out at a temperature of -10 ℃ to 60 ℃.

5. The method according to claim 2, characterized in that, The molar ratio of the acid to the dimer acid is 0.5 to 5:

1.

6. The method according to claim 2 or 5, characterized in that, The solvent for the ring-opening hydrolysis reaction is methanol, ethanol, methyl tert-butyl ether, and... N , N - at least one of dimethylformamide; and / or The temperature of the ring-opening hydrolysis reaction is room temperature to 100 ℃.

7. An electrolyte, characterized in that, The electrolyte contains an ammonium salt of the long-chain, hydroxyl-branched dicarboxylic acid as described in claim 1 and a solvent.

8. The electrolyte according to claim 7, characterized in that, In the electrolyte, the concentration of the ammonium salt of the long-chain hydroxyl-branched dicarboxylic acid is 10-30 wt%.

9. The electrolyte according to claim 7 or 8, characterized in that, The electrolyte has a pH value of 7-8.

10. The electrolyte according to claim 7 or 8, characterized in that, The solvent is at least one of ethylene glycol, glycerol, and γ-butyrolactone.

11. A method for preparing the electrolyte according to any one of claims 7-10, characterized in that, The method includes: dissolving the long-chain hydroxyl-containing branched dicarboxylic acid in the solvent, and then introducing ammonia gas.

12. The application of the electrolyte according to any one of claims 7-10 in aluminum electrolytic capacitors.

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