A high-rate long-cycle lead-acid battery negative electrode composite material and a preparation process thereof

Abstract

The application discloses a kind of high magnification long cycle lead-acid battery negative pole composite material and preparation process thereof, belong to lead-acid battery technical field.The process includes: lead powder, hexagonal boron nitride nanosheet, lead tartrate, conductive carbon black, barium sulfate and calcium fluoride are mixed according to proportion, polyvinyl alcohol aqueous solution is added to pulp, spray drying granulation is made, and heat treatment is carried out at 300~320 DEG C under inert atmosphere for 3~5h.The hexagonal boron nitride nanosheet is introduced into lead-acid battery negative pole system for the first time, and the hydrogen evolution side reaction is inhibited from the root;Lead tartrate is in-situ pyrolyzed to generate nano lead inlaid carbon matrix, and lead-carbon integrated interface is formed.Hexagonal boron nitride nanosheet, calcium fluoride and barium sulfate are synergistically constructed into permanent inert inorganic framework, and the active material densification is significantly delayed.The obtained composite material has excellent conductive network, higher hydrogen evolution overpotential and long cycle structural stability, and the cycle life is significantly improved under high magnification partial state of charge.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lead-acid storage batteries, in particular to a high-rate long-cycle lead-acid battery negative electrode composite material and a preparation process thereof. BACKGROUND

[0002] With the development of renewable energy storage systems such as solar energy and wind energy, and technologies such as hybrid electric vehicles and start-stop power sources, the working mode of lead-acid batteries has gradually changed from the traditional full-charge full-discharge to shallow cycle operation under high-rate partial state of charge (HRPSoC). Under this working mode, the negative active material repeatedly experiences the deposition and dissolution of lead sulfate, which is prone to generate coarse and difficult-to-dissolve lead sulfate crystals (i.e. irreversible sulfation), and the conductive network is continuously deteriorated, resulting in the increase of battery internal resistance, the attenuation of capacity, and the dramatic shortening of cycle life. For this reason, the industry has developed lead-carbon battery technology, which introduces carbon materials into the negative active material, utilizes the high conductivity and high specific surface area of carbon and the electrodeposition template effect of lead ions to delay sulfation and build a robust electronic transmission network, thereby improving the cycle capacity of the negative electrode under HRPSoC.

[0003] One of the more typical existing technologies involves mixing lead oxide powder, activated carbon, carbon nanotubes, barium sulfate, sodium lignosulfonate, and polytetrafluoroethylene emulsion in water to form a slurry. After spray drying and granulation, the slurry is heat-treated at 450–550°C under an inert atmosphere to obtain a lead-carbon composite material. Although this method, through the composite of lead powder and various carbon materials, suppresses excessive growth of lead sulfate grains to some extent and improves cycle performance, it still has the following drawbacks. First, there is the hydrogen evolution problem: during the final stage of charging or high-rate charging of lead-acid batteries, the negative electrode potential drops below the hydrogen evolution potential, triggering a hydrogen evolution side reaction. Although this method involves heat treatment at 450–550°C, causing some lead oxide to undergo carbothermic reduction to form metallic lead, this temperature range is insufficient to eliminate deep lattice defects and edge active sites in the carbon material. Secondly, the lead-carbon interface bonding problem: The carbothermic reduction reaction between lead oxide and carbon materials at 450~550℃ is a solid-solid reaction, with a slow reaction rate limited by the contact area. The resulting metallic lead is unevenly distributed on the carbon surface, and a significant portion of the lead particles are loosely bonded to the carbon matrix only through physical contact. During repeated dissolution-deposition cycles, this weak interface is easily degraded, and lead particles migrate and aggregate, re-exposing the conductive carbon network, thereby accelerating hydrogen evolution and the disintegration of active materials. Thirdly, the organic expanding agent failure problem: Sodium lignosulfonate is used as an organic expanding agent to inhibit lead sulfate grain growth and maintain the porosity of active materials in the early stages of battery cycling. However, sodium lignosulfonate is completely pyrolyzed and carbonized during high-temperature heat treatment at 450~550℃, significantly reducing or eliminating its grain control function, easily forming a dense primary lead sulfate layer, affecting subsequent cycle life. Fourthly, the binder carbonization product problem. Polytetrafluoroethylene (PTFE) decomposes at high temperatures, posing a risk of releasing toxic gases. Furthermore, the carbonized residues of its carbonization products have a loose structure and poor electronic conductivity. In the negative electrode, they not only fail to effectively enhance the conductive framework, but the remaining micropores may also become active areas for hydrogen evolution reactions, further exacerbating water loss.

[0004] Therefore, there is an urgent need to develop a new type of negative electrode composite material that can simultaneously achieve strong lead-carbon interfacial bonding, efficient suppression of hydrogen evolution, and long-lasting structural support to meet the stringent requirements of high-rate, long-cycle lead-acid batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a high-rate, long-cycle lead-acid battery anode composite material and its preparation process. This invention utilizes a lead-carbon integrated interface, introduces hexagonal boron nitride nanosheets as a long-lasting hydrogen evolution shielding agent and framework stabilizer, and employs low-temperature heat treatment to retain active functional groups and synergistically enhance the inorganic framework, ultimately achieving a significant leap in cycle life under high-rate partial charge conditions.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a process for preparing a high-rate, long-cycle lead-acid battery anode composite material, comprising the following steps: (1) By weight, 100 parts lead powder, 0.5-3 parts hexagonal boron nitride nanosheets, 5-15 parts lead tartrate, 2-8 parts conductive carbon black, 1-3 parts barium sulfate, and 0.5-1.5 parts calcium fluoride are dry-mixed to obtain a mixed powder. The hexagonal boron nitride (h-BN) nanosheets have a diameter of 50-500 nm and a thickness of 1-20 nm; the lead powder has an average particle size of 1-5 μm; the conductive carbon black is at least one of SuperP, acetylene black, or Ketjen black, preferably with a specific surface area of ​​50-1500 m². 2 / g of highly conductive carbon black; the barium sulfate is submicron-sized barium sulfate prepared by precipitation method; the calcium fluoride is micron-sized powder produced by chemical precipitation method.

[0007] (2) Dissolve polyvinyl alcohol (PVA) completely in deionized water to prepare a 2%~5% (w / w) aqueous solution of polyvinyl alcohol (PVA). The degree of polymerization of the polyvinyl alcohol is 1700~2000, and the degree of alcoholysis is 88%~99%.

[0008] (3) Gradually add the mixed powder obtained in step (1) to the polyvinyl alcohol (PVA) aqueous solution in step (2) while stirring. Keep the system temperature at 60~70℃ and continue stirring for 1~3 hours until a slurry with uniform composition and appropriate viscosity is formed. The total solid content of the slurry is controlled at 60%~75%.

[0009] (4) The slurry obtained in step (3) is granulated using a spray dryer. The inlet air temperature is controlled at 180~220℃ and the outlet air temperature is controlled at 80~100℃ to obtain black or gray-black spherical precursor particles. The average particle size is controlled at 30~120μm.

[0010] (5) Spread the precursor particles evenly in a high-temperature resistant container (such as an alumina boat), place it in a tube furnace, and heat it to 300-320°C at a heating rate of 2-5°C / min under a continuous atmosphere of high-purity nitrogen (above 99.99%) or argon, and hold it at this temperature for 3-5 hours. After the holding period, continue to purge the protective atmosphere and allow it to cool naturally to room temperature. Remove it and sieve it to obtain the high-rate long-cycle lead-acid battery negative electrode composite material.

[0011] In this invention, lead tartrate decomposes in situ at 300-320°C to produce metallic lead and carbon. These newly formed lead atoms first nucleate and grow into nanoscale lead particles in the surrounding organic carbonized matrix, which are then in situ coated by the amorphous carbon. Simultaneously, polyvinyl alcohol undergoes pyrolysis, resulting in hydroxyl dehydration and main chain breakage, generating water, small molecule hydrocarbons, and residual amorphous carbon raw materials. The lead powder particles, acting as a bulk inert matrix, have their surfaces uniformly covered with a carbon film during PVA carbonization, achieving metallurgical-grade bonding with the aforementioned in-situ generated nanoscale lead particles through this carbon film. This achieves the reconstruction of lead-carbon at the nano-molecular scale, creating a unified lead-carbon interface with significantly enhanced interfacial bonding strength, thus substantially improving the stability of the conductive network during repeated cycling.

[0012] As a preferred embodiment, the mass ratio of lead powder, hexagonal boron nitride nanosheets, lead tartrate, conductive carbon black, barium sulfate and calcium fluoride in step (1) is 100:1:10:5:2:1.

[0013] Preferably, the mass fraction of the polyvinyl alcohol aqueous solution in step (2) is 4%, and the polyvinyl alcohol used is PVA-1799.

[0014] Preferably, the stirring time in step (3) is 2 hours and the solid content of the slurry is 70%.

[0015] Preferably, the inlet temperature of the spray dryer in step (4) is 200°C and the outlet temperature is 90°C.

[0016] Preferably, in step (5), the temperature is increased to 310°C at 3°C / min and held for 4 hours.

[0017] Under these optimal conditions, the synergistic effect among the components is maximized, resulting in the best performance of the composite material.

[0018] The hexagonal boron nitride nanosheets are commercially available from Zhejiang Yameinami Technology Co., Ltd.

[0019] In this invention, hexagonal boron nitride (h-BN) nanosheets are a wide-bandgap (approximately 5.9 eV) insulating ceramic material that has traditionally been used in high-temperature lubrication, thermally conductive fillers, and electronic packaging. However, there have been no reports of its application in lead-acid battery anode materials to date.

[0020] This application introduces it into the above-mentioned low-temperature co-carbonization system, resulting in the following effects: (1) Selective and long-term hydrogen evolution inhibition. Due to its high surface energy and two-dimensional structure, h-BN sheets will spontaneously adsorb and spread on the high-energy edges and defects of newly formed carbon, forming a strong inert coating layer. Precisely passivates the active center of hydrogen evolution and prevents hydrogen evolution reaction. Compared with the defect of BCN in the prior art that will gradually decompose during cycling, the h-BN used in this invention has higher chemical stability and structural integrity, and can continuously play a role in inhibiting hydrogen evolution throughout the entire battery life cycle. (2) Permanent inorganic framework support. h-BN has excellent chemical inertness and electrochemical stability. Together with barium sulfate and calcium fluoride particles, which are also inert, it acts as a "permanent nanospacer" and framework node, physically preventing the fusion and coarsening of lead particles and the densification of active materials. This mechanism surpasses the traditional organic expansion agent (which is consumed in the early stage of use) or the single nucleation effect of barium sulfate. (3) The lamellar structure of h-BN can adsorb and separate lead powder particles in the slurry and in the early stage of heat treatment, preventing them from local sintering when they are close to the melting point of lead (327.5℃). This allows the present invention to be safely kept at a high temperature for a long time within the solid-state temperature window of 300~320℃ without worrying about the aggregation and flow of trace amounts of liquefied lead, thus ensuring the spherical morphology and uniformity of the precursor particles.

[0021] Secondly, the present invention also provides a high-rate, long-cycle lead-acid battery anode composite material prepared by the above-described process. The phase composition of this composite material includes: a metallic lead phase serving as the framework and main active material, derived from nano-lead produced by the pyrolysis of raw lead powder and lead tartrate; a carbon phase serving as the conductive framework and lead-carbon interface, derived from conductive carbon black and the pyrolytic carbon of lead tartrate and polyvinyl alcohol; a hexagonal boron nitride phase serving as a hydrogen evolution shield and structural stabilizer; and barium sulfate and calcium fluoride phases serving as an inert framework and nucleating agent.

[0022] In this invention, calcium fluoride is sparingly soluble in water and slightly soluble in acid, and can persist for a long time in the negative electrode active material. Introducing calcium fluoride into the negative electrode system as an inorganic additive, its sparingly soluble nature allows it to remain stably in the active material for a long time, which helps to control the deposition morphology of lead sulfate during cycling. When used in combination with h-BN and barium sulfate, it forms a long-lasting inorganic protective system.

[0023] Thirdly, the present invention also provides a lead-acid battery negative electrode using the above-mentioned composite material, which is manufactured by conventional paste, coating, curing, drying, and formation processes. Lead-acid batteries assembled from this negative electrode are particularly suitable as start-stop batteries, power batteries, or energy storage batteries.

[0024] This invention solves the problems of severe hydrogen evolution, weak interfacial bonding, expansion agent failure and high-temperature sintering in the prior art through the synergistic effect of in-situ pyrolysis of lead tartrate, selective coating with h-BN and low-temperature solid-state carbonization. The prepared composite material has extremely high electrical conductivity, extremely low hydrogen evolution activity and excellent cycle structure retention.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Significant hydrogen evolution suppression effect. By selectively coating the active sites of newly formed carbon materials with hexagonal boron nitride nanosheets, the hydrogen evolution current of the negative electrode is reduced, alleviating the problems of battery water loss and swelling, and extending the maintenance cycle and service life.

[0026] 2. Significantly improved high-rate cycle life. Under HRPSoC conditions of 60% state of charge and 1 A·s constant current, the battery's cycle life is also significantly improved, thanks to the synergistic effect of the integrated lead-carbon interface and the permanent inorganic framework.

[0027] 3. Low-temperature solid-state process is safe and energy-saving. The heat treatment temperature is only 300~320℃, which is much lower than the 450~550℃ of traditional lead-carbon materials, significantly reducing energy consumption and avoiding the melting of lead, emission of toxic gases and excessive decomposition of organic components at high temperatures. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation process of the present invention.

[0029] Figure 2 The graph shows a comparison of the linear sweep voltammetry (LSV) hydrogen evolution polarization curves of the electrode plates prepared from the negative electrode composite material obtained in Example 1 and the composite materials obtained in Comparative Examples 1 and 2.

[0030] Figure 3 This is a comparison graph showing the change in cycle life of the test cells assembled using the composite materials of Example 1 and Comparative Examples 1 and 2 as a function of high-rate partial state of charge (HRPSoC). Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are only for explaining the invention and not for limiting it. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] Example 1 A high-rate, long-cycle lead-acid battery anode composite material is prepared through the following steps (e.g.) Figure 1 (as shown) (1) Weigh 1000g of lead powder (average particle size 3μm), 15g of hexagonal boron nitride nanosheets (sheet diameter 100~300nm, thickness 3~8nm), 100g of lead tartrate, 50g of conductive carbon black SuperP, 20g of precipitated barium sulfate, and 10g of calcium fluoride, put them into a V-type mixer, mix at 30rpm for 40min to obtain mixed powder A.

[0034] (2) Add 40g PVA-1799 to 960g deionized water, heat to 90℃ and stir to dissolve completely, and after cooling, obtain 4wt% polyvinyl alcohol (PVA) aqueous solution B.

[0035] (3) Mixed powder A was slowly added to solution B under continuous stirring. The mixture was kept at 65°C using a water bath and stirred vigorously for 2 hours to form a uniform, particle-free black slurry C. The measured solid content was 70%.

[0036] (4) The slurry C was granulated using a centrifugal spray dryer. The inlet air temperature was set to 200℃ and the outlet air temperature to 90℃, and the feed rate was automatically adjusted according to the outlet air temperature. Grayish-black precursor particles D with good sphericity and an average particle size of about 80μm were collected.

[0037] (5) Place the precursor particles D in a corundum boat, put it into a tube furnace, evacuate the furnace, and then introduce high-purity nitrogen (99.999%) to maintain flow. Increase the temperature to 310°C at a rate of 3°C / min and hold for 4 hours. After the reaction is complete, allow it to cool naturally to room temperature under a nitrogen atmosphere and pass it through a 200-mesh sieve to obtain the negative electrode composite material of this invention, denoted as E1.

[0038] Example 2 The difference from Example 1 is that in step (1), the amount of hexagonal boron nitride nanosheets is changed to 5g, the amount of lead tartrate is changed to 150g, and other conditions remain unchanged. The resulting composite material is denoted as E2.

[0039] Example 3 The difference from Example 1 is that the heat treatment temperature in step (5) is changed to 320°C and the holding time is changed to 3 hours. The resulting composite material is denoted as E3.

[0040] Example 4 The difference from Example 1 is that in step (1), the conductive carbon black is replaced with acetylene black, and the amount is 80g; the mass fraction of the polyvinyl alcohol aqueous solution is changed to 2%; and in step (5), the heating rate is changed to 2℃ / min, the holding temperature is 300℃, and the holding time is 5h. The resulting composite material is denoted as E4.

[0041] Comparative Example 1 1000g of lead oxide powder, 30g of activated carbon, 10g of multi-walled carbon nanotubes, 20g of barium sulfate, 10g of sodium lignosulfonate, and 25g of PTFE emulsion with a solid content of 60% were mixed with an appropriate amount of water and stirred to form a slurry with a solid content of approximately 70%. The slurry was then spray-dried (under the same conditions as in Example 1). The resulting precursor was heated to 500°C at a rate of 5°C / min under a nitrogen atmosphere, held at that temperature for 2 hours, allowed to cool naturally, and then sieved to obtain composite material D1.

[0042] Comparative Example 2 Based on Example 1, no hexagonal boron nitride nanosheets were added, that is, the amount of hexagonal boron nitride used in step (1) was 0, and everything else was completely the same. The resulting composite material was denoted as D2.

[0043] Comparative Example 3 Based on Example 1, lead tartrate was replaced with lead oxide in equal molar amounts, and 2g of carbon black was added to balance the carbon content. Other steps remained unchanged, and the resulting composite material was denoted as D3.

[0044] Performance testing The composite materials prepared in each embodiment and comparative example were processed according to the same paste formulation (100 parts composite material, 12 parts deionized water, density 1.40 g / cm³). 3 Lead paste (containing 8 parts sulfuric acid and 0.3 parts short fibers) was prepared in a conventional paste-making machine and coated onto a conventional Pb-Ca-Sn alloy grid. After curing (50℃ / 95%RH, 24h; 75℃ low humidity, 24h) and drying (90℃, 12h), the final product had a density of 1.28 g / cm³. 3 A 2V / 20Ah experimental battery was prepared by performing a three-charge-two-discharge formation in sulfuric acid.

[0045] Hydrogen evolution performance test: Take the test negative plate after formation and fully charge (to remove the influence of the grid), at a density of 1.28 g / cm³. 3 Linear sweep voltammetry (LSV) was performed in sulfuric acid using Hg / Hg₂SO₄ (saturated K₂SO₄) as the reference electrode and a platinum sheet as the auxiliary electrode. The scan range was from -0.9V to -1.5V, and the scan rate was 0.5mV / s. The hydrogen evolution current at a potential of -1.2V (vs. Hg / Hg₂SO₄) was recorded.

[0046] HRPSoC Cyclic Performance Test: The test battery was subjected to constant current (1A·s) charge-discharge pulse cycles at 60% charge: 60s charging, 10s rest, 60s discharging, 10s rest. The cycle ended when the discharge voltage dropped to 1.75V. The number of cycles was recorded. At least 3 batteries were tested in each group, and the average value was taken.

[0047] The test results are listed in Table 1 below.

[0048] Table 1. Performance Comparison of Each Embodiment and Comparative Example From Table 1 and in combination Figure 2 , Figure 3 It can be clearly seen that: (1) Hydrogen evolution suppression effect: Compared with comparative examples 1-3, the hydrogen evolution current of examples 1-4 of the present invention is significantly reduced.

[0049] (2) HRPSoC cycle life: Compared with Comparative Examples 1-3, the number of cycles in Examples 1-4 of the present invention is all above 30,000.

[0050] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A preparation process for a high-rate, long-cycle lead-acid battery anode composite material, characterized in that, Includes the following steps: (1) Lead powder, hexagonal boron nitride nanosheets, lead tartrate, conductive carbon black, barium sulfate and calcium fluoride are mixed in a mass ratio of 100:(0.5~3):(5~15):(2~8):(1~3):(0.5~1.5) to obtain a mixed powder; the hexagonal boron nitride nanosheets have a diameter of 50~500nm and a thickness of 1~20nm; (2) Dissolve polyvinyl alcohol in deionized water to prepare a polyvinyl alcohol aqueous solution with a mass fraction of 2% to 5%; (3) The mixed powder is added to the polyvinyl alcohol aqueous solution and stirred at 60~70°C to form a slurry; (4) The slurry is spray-dried and granulated to obtain spherical precursor particles; (5) Under the protection of an inert atmosphere, the precursor particles are heated to 300-320°C at a rate of 2-5°C / min and kept at the temperature for 3-5 hours to generate nano-lead through in-situ pyrolysis of lead tartrate and form a lead-carbon integrated interface with carbon materials. After cooling, a high-rate long-cycle lead-acid battery negative electrode composite material is obtained.

2. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 1, characterized in that, The hexagonal boron nitride nanosheets mentioned in step (1) have a diameter of 100~300nm and a thickness of 2~10nm.

3. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 1, characterized in that, The average particle size of the lead powder mentioned in step (1) is 1~5μm.

4. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 1, characterized in that, The conductive carbon black mentioned in step (1) is at least one of SuperP, acetylene black, or Ketjen black.

5. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 1, characterized in that, In step (3), the solid content of the slurry is controlled at 60%~75%; the stirring time is 1~3 hours.

6. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 1, characterized in that, In step (4), the inlet temperature of the spray dryer is 180~220℃ and the outlet temperature is 80~100℃.

7. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 6, characterized in that, The average particle size of the precursor particles obtained in step (4) is 30~120μm.

8. The preparation process of a high-rate, long-cycle lead-acid battery negative electrode composite material according to claim 1, characterized in that, The inert atmosphere mentioned in step (5) is high-purity nitrogen or argon atmosphere; the heating rate is 3℃ / min, the holding temperature is 310℃, and the holding time is 4 hours.

9. A high-rate, long-cycle lead-acid battery negative electrode composite material, characterized in that, It is prepared by any one of the preparation processes described in claims 1 to 8.

10. A negative electrode for a lead-acid battery, characterized in that, It includes the high-rate, long-cycle lead-acid battery anode composite material as described in claim 9.

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