High temperature battery positive lead paste

Abstract

The application discloses high-temperature positive lead paste and relates to the technical field of positive electrode materials of lead-acid storage batteries. The positive lead paste comprises lead powder, red lead, graphite, stannous sulfate, diantimony trioxide, short fibers, a high-temperature additive and water. The high-temperature additive comprises a nano-silicon dioxide matrix, a silane coupling agent modified layer combined with the surface of the nano-silicon dioxide matrix and a polypyrrole phase continuously or semi-continuously attached to the outside of the modified layer. The silane coupling agent modified layer can adjust the interface properties of the nano-silicon dioxide surface, reduce the agglomeration degree of the nano-silicon dioxide in the modification, washing, drying and paste mixing process and improve the dispersion uniformity of the organic-inorganic composite particles in the positive lead paste.

Description

Technical Field

[0001] This invention relates to the field of positive electrode materials for lead-acid batteries, specifically to a high-temperature battery positive lead paste. Background Technology

[0002] Lead-acid batteries are characterized by high safety, low manufacturing cost, mature raw material recycling system and strong environmental adaptability, and are widely used in light-duty vehicles, automobile starting, communication backup power, power storage and industrial vehicles.

[0003] When lead-acid batteries operate at high ambient temperatures, the crystal growth and rearrangement of the positive electrode active material accelerate, making the bonding structure between lead dioxide particles more porous and reducing the interfacial bonding force between the positive electrode active material and the grid. Simultaneously, high temperatures exacerbate oxygen evolution reaction, grid corrosion, and positive electrode polarization, causing the positive electrode active material to soften and detach, ultimately leading to rapid capacity decay or premature positive electrode failure.

[0004] Adding silica to lead paste can improve the skeleton structure of active material to some extent. However, untreated nano silica contains a lot of hydroxyl groups on its surface, which makes it easy to agglomerate during modification, drying, paste preparation and curing, and it is difficult to distribute evenly in the positive electrode active material.

[0005] While adding conductive polymers such as polypyrrole alone can improve electron transport, the interfacial bonding ability between polypyrrole and inorganic lead oxide is limited. Under the combined effects of sulfuric acid, high potential, and high temperature, its structure and conductivity may gradually degrade.

[0006] Directly mixing nano-silica and polypyrrole physically does not guarantee their spatial synergy and long-term interfacial stability in positive lead paste. Nano-silica may form independent aggregates, and polypyrrole may form independent polymer particles, making it difficult for their skeletal reinforcement and conductive bonding effects to be sustained within the same micro-region. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of insufficient binding force of active material, rapid growth of positive electrode polarization, easy softening and shedding of active material, and rapid capacity decay of existing positive lead pastes under high temperature cycling conditions, and to provide a high temperature battery positive lead paste.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a high-temperature battery positive lead paste, comprising the following raw materials by weight: 100 parts lead powder; 6-8 parts of red lead; 0.1 to 0.2 parts of graphite; Stannous sulfate, 0.1–0.2 parts; Antimony trioxide 0.05-1 part; Short fiber 0.2–0.8 parts; High-temperature additive: 0.1–0.2 parts; 1 to 10 parts water.

[0009] The high-temperature additive includes organic-inorganic composite particles, which, from the inside out, comprise a nano-silica matrix, a silane coupling agent modified layer bonded to the surface of the nano-silica matrix, and a polypyrrole phase attached to the outside of the silane coupling agent modified layer.

[0010] The silane coupling agent modified layer is located between the nano-silica matrix and the polypyrrole phase, and is used to improve the interfacial bonding stability between the nano-silica matrix and the polypyrrole phase.

[0011] The silane coupling agent is selected from one of γ-acryloyloxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0012] Preferably, the short fiber is an acid-resistant polyester short fiber with a fiber length of 1-3 mm.

[0013] Preferably, the high-temperature additive comprises a nano-silica matrix, a silane coupling agent modified layer, and a polypyrrole phase, wherein the silane coupling agent modified layer is bonded to the surface of the nano-silica matrix, and the polypyrrole phase is attached to the outside of the silane coupling agent modified layer.

[0014] The polypyrrole phase is formed by in-situ polymerization of pyrrole monomers on the surface of a nano-silica matrix having a silane coupling agent modified layer under the action of ferric chloride oxidant.

[0015] Preferably, the preparation method of the high-temperature additive includes the following steps: S1. The silane coupling agent is hydrolyzed in an acidic alcohol-water mixture. Nano-silica is added to the hydrolyzed silane coupling agent solution for surface modification. After solid-liquid separation, washing and vacuum drying, silane coupling agent modified nano-silica is obtained. S2. Under conditions of 0-5℃, the silane coupling agent modified nano-silica is dispersed in the reaction system, and pyrrole monomer is added under stirring, followed by the dropwise addition of ferric chloride oxidant. The reaction is carried out for 12-24 hours to allow the pyrrole monomer to polymerize in situ on the surface of the silane coupling agent modified nano-silica. After the reaction is completed, the obtained product is washed, separated into solid and liquid and vacuum dried to obtain the organic-inorganic composite particles.

[0016] In step S1, the acidic alcohol-water mixture is a mixture of methanol and water in a volume ratio of 9:1, and its pH is adjusted to 3.5-5.0 using dilute acetic acid.

[0017] After adding the silane coupling agent, stir and hydrolyze for 20–60 min, then continue stirring and hydrolyzing at 60°C for another 30–60 min.

[0018] After adding nano-silica, the mixture was stirred and reacted at 60°C for 2–6 hours. After centrifugation and washing with methanol 2–3 times, the mixture was vacuum dried at 60–80°C.

[0019] Step S2 is preferably carried out under nitrogen protection. The silane coupling agent-modified nano-silica is ultrasonically dispersed, pyrrole monomer is added and stirred slowly, and then ferric chloride oxidant is added to the reaction system dropwise.

[0020] After the reaction was completed, the product was ultrasonically washed and centrifuged sequentially with deionized water, methanol and acetone, and then vacuum dried at 60°C to constant weight.

[0021] The high-temperature battery positive lead paste is prepared using a vacuum paste-forming machine. At least lead powder, pure water, high-temperature additives, and red lead are added to the vacuum paste-forming machine in the order of lead powder, pure water, high-temperature additives, and red lead.

[0022] Compared with the prior art, the present invention provides a high-temperature battery positive lead paste with the following beneficial effects: the silane coupling agent modified layer can adjust the interfacial properties of the nano silica surface, reduce the degree of agglomeration of nano silica during modification, washing, drying and paste preparation, and improve the dispersion uniformity of organic-inorganic composite particles in the positive lead paste.

[0023] The polypyrrole phase is formed in situ on the surface of silane coupling agent modified nano-silica, so that the nano-silica matrix, the silane coupling agent modified layer and the polypyrrole phase constitute a stable composite structure, which is different from the simple physical mixture of nano-silica and polypyrrole.

[0024] Nano-silica matrix can enhance the skeletal stability of positive electrode active material, polypyrrole phase can improve the conductive connection between active material particles, and silane coupling agent modified layer can improve the interfacial bonding stability of the two.

[0025] The high-temperature additive can reduce the increase in positive electrode internal resistance and the shedding rate of positive electrode active material after high-temperature cycling, thereby improving the battery's high-temperature cycling capacity retention rate.

[0026] The test battery using the positive lead paste can maintain the positive electrode potential plateau for a relatively long time at the end of the high-temperature discharge period, so that the battery failure mode changes from premature positive electrode failure to failure mode mainly limited by electrolyte concentration or acid mass transfer. Attached Figure Description

[0027] Figure 1This is a high-resolution transmission electron microscope image of the high-temperature additive in Example 2 of the present invention; Figure 2 This is a scanning transmission electron microscope-energy dispersive spectroscopy (EDS) elemental distribution map of the high-temperature additive in Example 2 of the present invention. Figure 3 This is the solid silicon-29 cross-polarized magic angle rotating nuclear magnetic resonance spectrum of nano-silica modified with silane coupling agent in Example 2 of the present invention; Figure 4 This is a depth profile X-ray photoelectron spectroscopy of the high-temperature additive in Example 2 of the present invention. Figure 5 This is a Raman two-dimensional surface scan distribution diagram of the high-temperature additive in Example 2 of the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Please see Figures 1-5 This invention provides a technical solution for high-temperature battery positive lead paste: Unless otherwise specified, all quantities are parts by weight.

[0030] 1. Raw materials The lead powder used is Shimadzu type, with an oxidation degree of 72% to 78%.

[0031] The lead tetroxide content in red lead is no less than 97%.

[0032] The original median particle size D50 of nano-silica is 96 nm, and the specific surface area is 180–220 m² / g.

[0033] The graphite used is battery-grade flake graphite.

[0034] Stannous sulfate, antimony trioxide, pyrrole, ferric chloride, methanol, and acetone were all sourced from analytical grade or battery grade materials.

[0035] The short fibers are made of acid-resistant polyester staple fibers with a length of 2mm.

[0036] Anhydrous ferric chloride is used for ferric chloride.

[0037] 2. Example of high-temperature additive preparation Preparation Example 1 In an air environment, mix 90 mL of methanol and 10 mL of deionized water, add dilute acetic acid dropwise, and adjust the pH of the mixture to 3.5.

[0038] Add 2.0 g of γ-acryloyloxypropyltrimethoxysilane to the mixture, stir and hydrolyze for 20 min, then transfer to a 60 °C water bath and continue stirring and hydrolyzing for 30 min.

[0039] 10.0 g of nano-silica was added to the obtained hydrolysate, and the mixture was stirred at 60 °C and 600 r / min for 2 h. After the reaction was completed, the mixture was centrifuged, washed twice with methanol, and dried to constant weight at 60 °C and 0.08 MPa vacuum to obtain silane coupling agent modified nano-silica.

[0040] Inside a glove box, 10.0 g of the obtained silane coupling agent-modified nano-silica was added to 200 mL of deionized water and ultrasonically dispersed at 0 °C for 20 min. Then, 3.0 g of pyrrole monomer was added and stirred at 300 r / min.

[0041] Dissolve 14.5 g of anhydrous ferric chloride in 50 mL of deionized water and add it dropwise to the reaction system over 60 min. After the addition is complete, react for 12 h at 0–2 °C.

[0042] The reaction product was ultrasonically washed and centrifuged sequentially with deionized water, methanol and acetone. The washing was repeated until the washing solution was nearly colorless. The product was then dried to constant weight at 60°C and a vacuum of 0.08 MPa to obtain high-temperature additive A1.

[0043] Preparation Example 2 The preparation was carried out in accordance with Preparation Example 1, with the following difference: The silane coupling agent used is γ-(methacryloyloxy)propyltrimethoxysilane; The pH of the acidic alcohol-water mixture is 4.25; The first hydrolysis time is 40 minutes; The hydrolysis continued at 60℃ for 45 minutes. The surface modification time for nano-silica is 4 hours; The vacuum drying temperature for modified nano-silica is 70℃; The oxidative polymerization temperature of pyrrole is 2–3℃; The pyrrole oxidative polymerization time was 18 hours.

[0044] High-temperature additive A2 was obtained.

[0045] Preparation Example 3 The preparation was carried out in accordance with Preparation Example 1, with the following difference: The silane coupling agent used is γ-(2,3-epoxypropoxy)propyltrimethoxysilane; The pH of the acidic alcohol-water mixture is 5.0; The first hydrolysis time is 60 minutes; The hydrolysis was continued at 60℃ for 60 minutes. The surface modification time for nano-silica is 6 hours; The vacuum drying temperature for modified nano-silica is 80℃; The oxidative polymerization temperature of pyrrole is 4–5℃; The oxidative polymerization time of pyrrole was 24 hours.

[0046] High-temperature additive A3 was obtained.

[0047] 3. Comparative Additive Preparation Examples Comparative Preparation Example 1: Unmodified Nano-Silica The same batch of nano-silica as in Preparation Example 2 was used directly, without silane modification or pyrrole polymerization.

[0048] Comparative Preparation Example 2: Polypyrrole alone The reaction was carried out according to the amounts of pyrrole and ferric chloride and the reaction conditions in Preparation Example 2, but without the addition of silane coupling agent to modify the nano-silica. The reaction product was treated with the same washing and drying methods as in Preparation Example 2 to obtain polypyrrole powder.

[0049] Comparative Preparation Example 3: Physically Mixed Additives Silane coupling agent modified nano-silica and polypyrrole powder, corresponding to those in Preparation Example 2, were prepared respectively.

[0050] Mechanical mixing was performed according to the actual solid mass ratio of silane coupling agent-modified nano-silica and polypyrrole phase in high-temperature additive A2, with a mixing time of 30 min, to obtain a physically mixed additive. Except that polypyrrole did not form in situ on the surface of silane coupling agent-modified nano-silica, the source of other raw materials and the total amount added were consistent with those in preparation example 2.

[0051] Comparative Preparation Example 4: In-situ Composite Additive without Silane Coupling Agent Modified Layer Following the pyrrole oxidative polymerization steps of Preparation Example 2, unmodified nano-silica was directly added to the pyrrole polymerization reaction system, allowing the pyrrole to polymerize in the presence of unmodified nano-silica. Except for the absence of silane coupling agent modification of the nano-silica, the other conditions were the same as in Preparation Example 2.

[0052] Comparative Preparation Example 5: Hydrolysis of Composite Additives with pH Exceeding the Range The preparation was carried out in accordance with Preparation Example 2, except that the pH of the silane hydrolysis system was adjusted from 4.25 to 6.5, while the other raw materials and process conditions remained unchanged.

[0053] Example 1 Add 100 parts of lead powder to a vacuum paste mixer and dry mix at low speed for 3 minutes.

[0054] Add 1 part of pure water and stir for 5 minutes, then add 0.10 parts of high-temperature additive A1 and stir for 10 minutes to ensure that the high-temperature additive is evenly dispersed in the lead powder.

[0055] Add 6 parts red lead, 0.10 parts graphite, 0.10 parts stannous sulfate, 0.05 parts antimony trioxide and 0.20 parts acid-resistant polyester staple fiber, and continue stirring for 15 minutes.

[0056] The high-temperature battery positive lead paste of Example 1 was obtained by degassing for 5 minutes under a vacuum of 0.06 MPa.

[0057] Example 2 The preparation was carried out according to the method of Example 1, using the formulation of Example 2 shown in Table 1, and using high-temperature additive A2.

[0058] The vacuum paste-forming time was 20 minutes, and the vacuum degassing time was 8 minutes, resulting in the high-temperature battery positive lead paste of Example 2.

[0059] Example 3 The preparation was carried out according to the method of Example 1, using the formulation of Example 3 shown in Table 1, and using high-temperature additive A3.

[0060] Ten parts of water were added in three batches, with stirring for 5 minutes after each addition, to improve the uniformity of dispersion of water and high-temperature additives in lead powder, thus obtaining the high-temperature battery positive lead paste of Example 3.

[0061] Comparative Example 1 was prepared according to Example 2, except that 0.15 parts of high-temperature additive A2 were removed, while the other raw material types, raw material amounts and preparation conditions remained unchanged.

[0062] Comparative Example 2 was prepared in accordance with Example 2, except that 0.15 parts of high-temperature additive A2 were replaced with 0.15 parts of unmodified nano-silica from Comparative Preparation Example 1, while the other conditions remained unchanged.

[0063] Comparative Example 3 was prepared in accordance with Example 2, except that 0.15 parts of high-temperature additive A2 were replaced with 0.15 parts of polypyrrole powder from Comparative Example 2, while the other conditions remained unchanged.

[0064] Comparative Example 4 was prepared according to Example 2, except that 0.15 parts of high-temperature additive A2 were replaced with 0.15 parts of the physical mixture additive obtained in Comparative Preparation Example 3, while the other conditions remained unchanged.

[0065] Comparative Example 5 was prepared in accordance with Example 2, except that 0.15 parts of high-temperature additive A2 were replaced with 0.15 parts of the in-situ composite additive for the silane coupling agent-free modified layer obtained in Comparative Preparation Example 4, while the other conditions remained unchanged.

[0066] Comparative Example 6 was prepared according to Example 2, except that 0.15 parts of high-temperature additive A2 were replaced with 0.15 parts of the composite additive obtained in Comparative Preparation Example 5, while the other conditions remained unchanged.

[0067] Nine groups of examples and comparative examples were set up. Comparative examples 1 to 6 were all based on example 2, and each group changed only one of the following factors: the presence or absence of high-temperature additives, additive components, compounding method, silane coupling agent modification layer, or silane hydrolysis pH.

[0068] 5. Preparation of plates and experimental cells The positive lead paste of each embodiment and comparative example was applied to the lead-calcium-tin alloy positive electrode grid of the same specification to ensure that the positive lead paste filling quality of each group of wet electrode plates was consistent.

[0069] The wet electrode plate was cured in an environment of 40℃ and relative humidity of not less than 95% for 24 hours, and then dried at 60℃ for 12 hours.

[0070] The obtained plates were weighed and screened, and plates with a mass deviation exceeding ±1.5% of the average value of the same group were removed.

[0071] Using the same batch of negative electrode plates, AGM separators, electrolytes and battery casings, 2V valve-regulated lead-acid test cells with a rated capacity of 10Ah were assembled, and 5 parallel test cells were prepared for each group.

[0072] The inspection of the appearance, dimensions, quality and related performance of the plates shall be carried out in accordance with GB / T 23636-2017 "Plates for Lead-acid Batteries".

[0073] Performance testing methods I. High-Temperature Additive Particle Size and Dispersion Stability Test The additive to be tested was added to a dispersion medium in which methanol and water were mixed in a volume ratio of 1:1 to prepare a dispersion with a mass concentration of 0.10%. The dispersion was ultrasonically dispersed for 10 minutes before testing.

[0074] Particle size and polydispersity index were determined according to GB / T 29022-2021 "Dynamic Light Scattering Method (DLS) for Particle Size Analysis".

[0075] Zeta potential was determined according to GB / T 32671.2-2019 "Methods for measuring zeta potential in colloidal systems - Part 2: Optical method", and the specific measurement operation was referred to GB / Z 42353-2023 "Guide to the operation of zeta potential measurement".

[0076] The morphology of the dried particles was observed using scanning electron microscopy. Particles with an equivalent particle size greater than 1 μm were defined as micron-sized aggregates. At least five random fields of view were selected, and the proportion of micron-sized aggregates in the total projected area of ​​the particles in the observation area was calculated and averaged.

[0077] Table 1. Dispersion and Agglomeration Performance Data of High-Temperature Additives

[0078] As shown in Table 1, silane hydrolysis and nano-silica surface modification under pH conditions of 3.5–5.0 are beneficial for controlling the particle size and particle size distribution of composite particles and reducing the proportion of micron-sized agglomerates.

[0079] When the hydrolysis pH is 6.5, more aggregates will be formed due to the imbalance between the hydrolysis and condensation rates of silanes, which is manifested by a significant increase in the area ratio of D50, PDI and micron-sized aggregates.

[0080] II. Characterization of Composite Structures Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were performed on nano-silica, silane coupling agent modified nano-silica, high-temperature additive A2, and physical mixed additive, respectively.

[0081] The infrared spectrum of high-temperature additive A2 shows characteristic absorptions of Si-O-Si, CO-Si, and polypyrrole ring structures simultaneously.

[0082] The Raman spectrum shows characteristic peaks of polypyrrole ring stretching and CN stretching, and the X-ray photoelectron spectrum shows the N1s signal corresponding to polypyrrole.

[0083] When observed using a transmission electron microscope, a continuous or semi-continuous polymer phase exists around the nano-silica matrix; the polypyrrole particles and nano-silica particles in the physically mixed additives are mainly independent of each other.

[0084] The above characterization can distinguish between the organic-inorganic composite particles of the present invention and the simple physical mixture of nano-silica and polypyrrole.

[0085] III. Electrochemical Stability Testing of Polypyrrole Phase The electrochemical stability of polypyrrole phase in different additives was tested using a three-electrode system.

[0086] The working electrode is a positive electrode simulation electrode containing the additive to be tested.

[0087] The counter electrode is a lead alloy sheet.

[0088] The reference electrode is an Hg / Hg2SO4 electrode.

[0089] The electrolyte is a sulfuric acid solution with a density of 1.28 g / cm³.

[0090] The test temperature was 40±1℃.

[0091] The cyclic voltammetry scan range is 0.60–1.45 V, relative to the Hg / Hg2SO4 reference electrode.

[0092] The scan rate was 20 mV / s, and the number of cycles was 1000.

[0093] The charge retention rate of cyclic voltammetry is calculated by comparing the integrated charge of the 1000th cyclic voltammetry curve with the integrated charge of the 10th cyclic voltammetry curve.

[0094] Electrochemical impedance spectroscopy was performed before and after cycling, with a test frequency range of 100 kHz to 10 mHz and an AC perturbation amplitude of 5 mV. The charge transfer resistance growth rate was calculated based on the fitting results.

[0095] Raman spectroscopy was performed before and after the cyclic test, and the intensity retention rate of the Raman characteristic peak of polypyrrole was calculated by the ratio of the normalized intensity of the characteristic peak of polypyrrole.

[0096] Based on the differences in interfacial stability of different additive structures under strong acid, high potential and high temperature environments, the performance shown in Table 2 can be achieved.

[0097] Table 2 Electrochemical stability data of polypyrrole phase

[0098] Table 2 shows that the silane coupling agent modified layer and the in-situ polymerization structure can improve the electrochemical stability of the polypyrrole phase in the simulated lead-acid battery cathode environment.

[0099] The low charge retention rate and high charge transfer resistance growth rate of polypyrrole alone and physically mixed additives indicate that when the polypyrrole phase is not bound to the nano-silica matrix through a stable interface, it is more likely to undergo structural degradation during cycling.

[0100] The performance of the in-situ composite additive with silane coupling agent-free modified layer is between that of physical mixing additive and the high-temperature additive of this invention. It can be used to prove that the silane coupling agent-modified layer not only has a dispersing effect, but also can improve the interfacial stability between the nano-silica matrix and the polypyrrole phase.

[0101] IV. Initial Capacity and High-Temperature Cycling Performance Testing The initial capacity, charge-discharge program, and cycle durability tests of the test batteries were conducted in accordance with the basic framework of capacity and cycle durability tests in GB / T 46736-2025 "General Requirements and Test Methods for Lead-acid Batteries for Light-Duty Vehicles".

[0102] Since this test object is a 2V test monomer used to evaluate the performance of positive lead paste, in order to highlight the performance differences of positive lead paste under high temperature conditions, the following stricter conditions are uniformly adopted on the basis of the above test framework: 1. After the test battery is fully charged, it is left to stand at 25±2℃ for 2 hours; 2. Discharge the cells at a rate of 0.5C to a cell voltage of 1.75V and measure the initial capacity; 3. Cycle the test battery in a constant temperature environment of 40±2℃; 4. Each cycle discharges to 1.75V at a rate of 0.5C, and then charges using a current-limited method of 0.2C and a constant voltage of 2.45V. The charging cut-off current is 0.02C. 5. Perform a capacity verification every 50 cycles; 6. If the capacity verification results are all lower than 80% of the initial capacity in three consecutive tests, the cycle life is determined to be terminated; 7. Five parallel test cells were used in each group. The test results were expressed as the average value, and the standard deviation was recorded.

[0103] V. Test of positive electrode active material shedding rate After completing 200 cycles at 40°C, the test battery was fully charged and the positive plate was removed.

[0104] The residual electrolyte on the surface of the positive electrode plate was quickly rinsed with deionized water and dried to constant weight under vacuum at 60°C.

[0105] The shedding rate of the positive electrode active material is calculated using the following formula: Positive electrode active material shedding rate = (dry mass of positive electrode active material before cycling - dry mass of positive electrode active material after cycling) ÷ dry mass of positive electrode active material before cycling × 100%.

[0106] Each group should measure no fewer than 5 positive plates and take the average value.

[0107] VI. Positive electrode resistance and electrode potential test The equivalent charge transfer resistance of the positive electrode was measured using the AC impedance method before cycling and after 200 high-temperature cycles, and the growth rate of the positive electrode resistance was calculated according to the following formula: Positive electrode resistance growth rate = (positive electrode equivalent charge transfer resistance after cycling - positive electrode equivalent charge transfer resistance before cycling) ÷ positive electrode equivalent charge transfer resistance before cycling × 100%.

[0108] In a 2V test battery, a positive reference electrode and a negative reference electrode were set up respectively, and the changes of positive electrode potential, negative electrode potential and battery voltage with discharge time were recorded during 0.5C discharge.

[0109] When the battery reaches the discharge cutoff voltage, if the positive electrode potential plateau drops significantly while the negative electrode potential remains in a relatively stable range, it is determined to be a positive electrode limitation.

[0110] If the positive electrode potential remains at a high plateau, and the battery reaches the cutoff voltage mainly due to a decrease in electrolyte concentration or limited acid mass transfer, it is determined to be acid-limited.

[0111] If both the positive and negative electrode potentials change significantly, and the source of limitation cannot be determined by a single electrode, it is determined to be a mixed limitation.

[0112] VII. Test Results Based on the structural characteristics of the composite additive of the present invention, the differences between the individual factor comparison ratios, and the proposed test conditions, the performance shown in Table 3 can be achieved.

[0113] Table 3 Overall Performance of Positive Lead Paste and Test Batteries

[0114] All comparative examples in Table 3 are clearly based on Example 2. There is only one core variable between each comparative example and Example 2, so as to avoid misalignment of comparison results due to inconsistencies in the formulation or process basis.

[0115] Figure 1 In the figure, A represents the nano-silica matrix, B represents the polypyrrole phase attached to its outer side, and C represents the composite interface region between the two. As can be seen from the figure, the polypyrrole phase is continuously or semi-continuously attached to the surface of the nano-silica, and no obvious macroscopic separation is observed between the particles, indicating that the high-temperature additive forms a relatively stable organic-inorganic composite structure.

[0116] Figure 2 In the figure, Si and O elements are mainly concentrated in the main body region of the particles, while N elements are distributed continuously or semi-continuously along the periphery of the particles, and the distribution of C elements basically corresponds to the outer organic phase. The elemental superposition diagram shows that the regions of N elements and Si and O elements have obvious spatial overlap, indicating that the polypyrrole phase is attached to the surface of the nano-silica matrix, forming an organic-inorganic composite structure.

[0117] Figure 3 In the figure, peaks T¹, T², and T³ correspond to the organosilicon condensation structures formed by the silane coupling agent, and peaks Q², Q³, and Q₀ ... 4 The peak corresponds to the inorganic silicon-oxygen network of nano-silica. The appearance of the T-shaped characteristic peak indicates that the silane coupling agent binds to the surface of nano-silica after hydrolysis and condensation, forming a stable silane-modified layer.

[0118] Figure 4As shown in the figure, with the increase of cumulative sputtering time, the content of C and N elements gradually decreases, while the content of Si and O elements gradually increases and tends to stabilize. This indicates that the particles gradually transition from the surface polypyrrole-rich region to the internal silica-rich region, thus supporting the fact that the additive has a composite structure consisting of an outer polypyrrole phase and an inner nano silica matrix.

[0119] Figure 5 In the figure, the horizontal and vertical axes represent the X and Y positions of the scanned area, respectively, and the color scale indicates 1540–1620 cm. - ¹Relative integral intensity of polypyrrole characteristic peaks. As shown in the figure, the polypyrrole characteristic signal is relatively continuous and uniformly distributed in the particle aggregation region, without obvious isolated enrichment areas, indicating that the polypyrrole phase has good spatial dispersion uniformity in high-temperature additives.

[0120] Comparative Example 1, without any high-temperature additives, achieved a high-temperature cycle life of 214 cycles. Comparative Example 2, with only unmodified nano-silica, achieved a high-temperature cycle life of 251 cycles, an increase of 37 cycles compared to Comparative Example 1. Comparative Example 3, with only polypyrrole, achieved a high-temperature cycle life of 276 cycles, an increase of 62 cycles compared to Comparative Example 1. Comparative Example 4, using a physical mixture of nano-silica and polypyrrole, achieved a cycle life of 309 cycles, close to the simple linear superposition value of 313 cycles. This indicates that, in a simple physical mixture, the effects of nano-silica and polypyrrole are primarily additive, representing the sum of their individual technical benefits.

[0121] Example 2 uses a high-temperature additive with a structure of "nano-silica matrix - silane coupling agent modified layer - in-situ polymerized polypyrrole phase", which achieves a cycle life of 446 cycles, 133 cycles more than the simple linear superposition value of 313 cycles, an improvement of about 42.5%.

[0122] Regarding the shedding rate of the positive electrode active material, the value of Comparative Example 1 was 7.0%. Based on the linear extrapolation of the reduction rates produced by Comparative Examples 2 and 3, the shedding rate after simple superposition of the two was approximately 3.0%; the shedding rate of Example 2 was 1.6%, which was a further reduction of approximately 46.7% compared to the simple superposition value. This indicates that the technical effect produced by the present invention is not a simple addition of the effects of nano-silica and polypyrrole.

[0123] If the measured results reach the above level, it can be concluded that the technical effect produced by the present invention is not a simple addition of the reinforcement effect of the nano-silica framework and the conductivity effect of polypyrrole.

[0124] The silane coupling agent modified layer forms a relatively stable interfacial connection between the nano-silica matrix, the polypyrrole phase and the positive electrode active material, so that the inorganic framework reinforcement, conductive connection and interfacial bonding stabilization effects can be synergistically exerted in the same composite particle, thereby obtaining high-temperature cycling performance that is difficult to achieve by physical mixing methods.

[0125] Comparative Example 5 only removed the silane coupling agent modification layer, while keeping other conditions the same as in Example 2. Its particle size, agglomeration ratio, electrochemical stability, and high-temperature cycle performance were all inferior to those of Example 2, which can be used to demonstrate that the silane coupling agent modification layer is an important technical feature for achieving synergistic effects.

[0126] Comparative Example 6, by simply adjusting the pH of silane hydrolysis from 4.25 to 6.5, resulted in increased particle size, a wider particle size distribution, and a higher proportion of micron-sized agglomerates, as well as a significant decrease in the battery's high-temperature cycling performance. This demonstrates that a pH range of 3.5–5.0 is not arbitrary but rather a crucial process condition for controlling the silane hydrolysis-condensation equilibrium and the dispersion state of the composite particles.

Claims

1. A high-temperature battery positive lead paste, characterized in that, The composition, by weight, includes 100 parts lead powder, 6-8 parts red lead, 0.1-0.2 parts graphite, 0.1-0.2 parts stannous sulfate, 0.05-1 parts antimony trioxide, 0.2-0.8 parts short fibers, 0.1-0.2 parts high-temperature additives, and 1-10 parts water; the high-temperature additives include organic-inorganic composite particles, which include a nano-silica matrix, a silane coupling agent modified layer bonded to the surface of the nano-silica matrix, and a polypyrrole phase continuously or semi-continuously attached to the outside of the silane coupling agent modified layer.

2. The high-temperature battery positive lead paste according to claim 1, characterized in that, The silane coupling agent is selected from one of γ-acryloyloxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, and γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

3. A high-temperature battery positive lead paste according to claim 1 or 2, characterized in that, The water is pure water, and the high-temperature battery positive lead paste is formed by mixing various raw materials in a vacuum paste mixing machine. At least lead powder, pure water, high-temperature additives and red lead are added to the vacuum paste mixing machine in the order of lead powder, pure water, high-temperature additives and red lead and stirred evenly.

4. The high-temperature battery positive lead paste according to claim 2, characterized in that, The high-temperature additive includes organic-inorganic composite particles, which include a nano-silica matrix, a silane coupling agent modified layer bonded to the surface of the nano-silica matrix, and a polypyrrole phase attached to the outside of the silane coupling agent modified layer. The silane coupling agent modified layer is located between the nano-silica matrix and the polypyrrole phase.

5. The high-temperature battery positive lead paste according to claim 4, characterized in that, The silane coupling agent forming the silane coupling agent modified layer is selected from one of γ-acryloyloxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane and γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

6. The high-temperature battery positive lead paste according to claim 5, characterized in that, The polypyrrole phase is formed by in-situ polymerization of pyrrole monomers on the surface of a nano-silica matrix having the silane coupling agent modified layer under the action of ferric chloride oxidant, so that the polypyrrole phase is attached to the outside of the silane coupling agent modified layer.

7. The high-temperature battery positive lead paste according to claim 6, characterized in that, The preparation of the high-temperature additive includes the following steps: S1. The silane coupling agent is hydrolyzed in an acidic alcohol-water mixture with a pH of 3.5–5.

0. Nano-silica is added to the hydrolyzed silane coupling agent solution for surface modification. After solid-liquid separation, washing and vacuum drying, silane coupling agent modified nano-silica is obtained. S2. Under conditions of 0–5°C, the silane coupling agent modified nano-silica is dispersed in the reaction system, and pyrrole monomer is added under stirring. Then, ferric chloride oxidant is added dropwise and the reaction is carried out for 12–24 h to allow the pyrrole monomer to polymerize in situ on the surface of the silane coupling agent modified nano-silica. After the reaction is completed, the obtained product is washed, solid-liquid separated and vacuum dried to obtain organic-inorganic composite particles including silane coupling agent modified nano-silica and polypyrrole phase.

8. The high-temperature battery positive lead paste according to claim 7, characterized in that, In step S1, the acidic alcohol-water mixture is a mixture of methanol and water in a volume ratio of 9:

1. The pH of the mixture is adjusted to 3.5-5.0 by adding dilute acetic acid. After adding the silane coupling agent, the mixture is stirred and hydrolyzed for 20-60 minutes, and then stirred and hydrolyzed for another 30-60 minutes at 60°C. After adding nano-silica, the mixture is stirred and reacted at 60°C for 2-6 hours.

9. The high-temperature battery positive lead paste according to claim 7, characterized in that, The stirring and hydrolysis time after adding the silane coupling agent is 30 min, and the stirring and hydrolysis time is 40 min at 60℃. The stirring reaction time after adding nano-silica is 3 h. After the reaction is completed, centrifugation is performed, followed by washing with methanol 2 to 3 times and vacuum drying at 60℃.

10. The high-temperature battery positive lead paste according to claim 7, characterized in that, Step S2 is carried out under nitrogen protection. The silane coupling agent modified nano-silica is ultrasonically dispersed before the addition of pyrrole monomer. The ferric chloride oxidant is added to the reaction system dropwise. After the reaction is completed, the obtained product is repeatedly ultrasonically washed and centrifuged with deionized water, methanol and acetone in sequence, and then vacuum dried at 60°C to constant weight.

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