Dry powder bonded film electrode, method of making and lead acid battery employing same

Abstract

This invention provides a dry-process powder-bonded thin-film electrode for lead-acid batteries and its preparation method. Addressing the acidic environment of lead-acid battery systems and the high-density characteristics of lead-based materials, this invention combines raw material selection with fully dry process control. A mixed dry powder, including lead-based active materials, conductive agents, and binders, obtained through low-speed dry mixing, is directly formed into an electrode film on a current collector. Then, hot-pressing is used to in-situ trigger the fibrous bonding material of the binder to form a composite film and achieve electrode film densification. This significantly improves the interfacial bonding force and structural uniformity of the electrode, solving technical problems such as solvent pollution and high energy consumption in traditional wet processes, and the inapplicability of existing dry preparation processes for lithium battery electrodes to the lead-acid battery field. This provides a new approach for the high-performance and green manufacturing of lead-acid batteries.

Description

Technical Field

[0001] This invention relates to the field of lead-acid battery technology, and in particular to a dry powder-bonded thin-film electrode, its preparation method, and a lead-acid battery using the same electrode. Background Technology

[0002] Lead-acid batteries occupy an important position in energy storage and starting power sources due to their advantages such as low cost, high safety, and mature recycling systems. However, the traditional manufacturing process of lead-acid battery electrodes usually involves gravity casting of grids coated with thick lead paste, which has drawbacks such as low utilization of active materials, poor rate performance, and short cycle life.

[0003] Chinese patent CN202310136648.0 discloses a method for preparing a film electrode for lead-acid batteries, comprising the following steps: adding a binder to the lead paste to be prepared; rolling the lead paste containing the binder onto a lead sheet to form a lead paste film layer; immersing the lead sheet and the attached lead paste film layer together in a sulfuric acid solution; removing and curing; and drying; wherein the binder is a polytetrafluoroethylene emulsion or a binder containing a polytetrafluoroethylene emulsion. Unlike existing technologies that attach polymer films to the surface of lead-acid battery plates, this invention yields a thin-film electrode with thin thickness, uniform dispersion of active material, large contact area between the active material and the current collector, and good conductivity, offering advantages such as high-rate charge-discharge cycling.

[0004] However, the essence of the above-mentioned existing technologies is still a solvent-based wet / mixed process, which cannot get rid of the problems of cost, environmental protection and energy consumption caused by the use of solvents; and its binder system is relatively complex, and there is still room for optimization of the long-term stability of PTFE emulsion in acidic electrolyte and its influence on electrode internal resistance.

[0005] Chinese patent CN202210476320.9 discloses a dry electrode preparation method, comprising fiberizing at least one material selected from electrode active material, conductive agent, and binder to form a fibrous material, wherein the fibrous material includes the binder; covering the surface of the current collector with the fibrous material and the remaining materials to form a semi-finished electrode sheet; and calendering the semi-finished electrode sheet to form a finished electrode sheet. By covering the current collector surface with the fibrous material and the remaining materials, the electrode active material and conductive agent can be dispersed on the binder, and the fibrous binder can enhance the bonding between the electrode active material, conductive agent, and current collector, thereby enhancing the strength of the formed semi-finished electrode sheet, improving the electrode uniformity, reducing the requirement for binder content, and increasing the energy density of the battery.

[0006] The aforementioned dry electrode manufacturing technology, as an emerging process, is currently mainly applied in the field of lithium-ion batteries. Its raw materials and process system are designed for lithium battery systems with organic electrolyte environments and lightweight active materials. However, lead-acid battery systems are completely different from lithium battery systems in terms of material characteristics and reaction mechanisms. Due to its strongly acidic electrolyte (such as sulfuric acid), high-density lead-based active materials (such as lead powder particles that are large and irregular, posing compatibility issues with binder networks), and volume changes during charging and discharging, lead-acid batteries present unique challenges to the corrosion resistance, mechanical strength, and interface stability of the electrodes. This makes it impossible to directly apply lithium battery dry electrode manufacturing technology to lead-acid batteries, as problems such as binder degradation, difficulty in uniform film formation, and increased interfacial impedance may occur. Summary of the Invention

[0007] One objective of this invention is to address the shortcomings of existing technologies by providing a method for preparing a dry powder-bonded thin-film electrode for lead-acid batteries. Targeting the acidic environment of lead-acid battery systems and the high-density characteristics of lead-based materials, this method combines raw material selection with fully dry process control. A mixed dry powder, including lead-based active materials, conductive agents, and binders, obtained through low-speed dry mixing, is directly formed into an electrode film on a current collector. Then, hot-pressing is used to trigger in-situ dry composite film formation of the binder and achieve electrode film densification. This significantly improves the interfacial bonding force of the electrode and solves the technical problems of solvent pollution, high energy consumption, and the inapplicability of existing dry preparation processes for lithium battery electrodes to the lead-acid battery field. This provides a new approach for the high-performance and green manufacturing of lead-acid batteries.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a dry powder-bonded thin-film electrode includes the following steps: S1, Dry mixing: Lead-based active material, conductive agent and solid binder powder are mixed at low speed under inert gas protection to obtain mixed dry powder; S2, the mixed dry powder is applied to the surface of the current collector by electrostatic spraying or dry calendering to form an electrode film; S3, Hot pressing: Hot pressing is performed at 160~220℃ and 10~50MPa for 1~5min. During this process, the adhesive undergoes in-situ fibrosis, which extends and entangles with each other to form a three-dimensional network structure, thereby encapsulating and bonding the active material and conductive agent together. The mixed dry powder particles are also compacted to densify the electrode film.

[0009] As an improvement, in step S1, the lead-based active material is surface-coated and modified, with the coating layer being carbon or an amorphous metal oxide, and the coating layer thickness being 1~10 nm.

[0010] As an improvement, the lead-based active material is made of lead powder or lead oxide; the conductive agent is made of acetylene black or carbon nanotubes.

[0011] As an improvement, in step S1, the adhesive comprises polytetrafluoroethylene and thermoplastic polyurethane, and the mass ratio of the two is 70~99:30~1.

[0012] Preferably, the mass ratio of polytetrafluoroethylene to thermoplastic polyurethane is 85~95:15~5.

[0013] As an improvement, the thermoplastic polyurethane is a polyether type and is surface modified with nano-silica.

[0014] As an improvement, in step S1, a shear mixer is used for low-speed dry mixing, with a mixing speed of 1000~3000 rpm and a mixing time of 10~30 min.

[0015] As an improvement, in step S2, the voltage of the electrostatic spraying is 20~60kV, and the electrode film thickness is controlled to be 50~150μm by the voltage and the powder feeding rate.

[0016] Preferably, the electrode film thickness is 70~120μm.

[0017] In step S2, the powder feeding rate of electrostatic spraying is gradually reduced or the pressure of dry calendering is gradually reduced so that the porosity of the electrode film is gradually increased from the current collector side outward.

[0018] As an improvement, in step S2, the current collector is made of stainless steel foil and has undergone surface modification treatment such as roughening or conductiveing.

[0019] As an improvement, the surface treatment method of the current collector includes plasma etching, electrochemical deposition of a conductive carbon layer, or growth of a nano-oxide layer.

[0020] The second objective of this invention is to provide a dry-process powder-bonded thin-film electrode for lead-acid batteries. The active material layer has a porous thin-film electrode structure with a gradient distribution of pores and adjustable porosity within a certain range. The active material layer has high peel strength with the current collector, strong interfacial bonding force, and good structural uniformity. Therefore, the electrode has outstanding advantages such as short ion transport path, high rate performance, and long cycle life, solving the technical problems of high resistance, poor rate performance, and easy detachment of active material caused by the thick lead paste in existing lead-acid battery electrodes.

[0021] To achieve the above objectives, the present invention provides the following technical solution: A dry powder-bonded thin-film electrode includes a stainless steel current collector and an electrode active material layer formed on the surface of the stainless steel current collector, wherein the electrode active material layer has a porous thin-film structure.

[0022] As an improvement, the porosity of the electrode active material layer is adjustable in the range of 20% to 40%, and its porosity increases in a gradient from the stainless steel current collector side outwards.

[0023] As an improvement, the peel strength between the electrode active material layer and the stainless steel current collector is ≥20 N / m, and the 1C capacity retention rate is ≥90%.

[0024] The third objective of this invention is to provide a lead-acid battery with outstanding advantages such as a short ion transport path, high rate performance, and long cycle life.

[0025] To achieve the above objectives, the present invention provides the following technical solution: A lead-acid battery, wherein the positive and / or negative electrodes are dry powder-bonded thin film electrodes as described in any one of claims 10-12.

[0026] As an improvement, the battery retains ≥85% of its capacity after 600 cycles at 0.2C rate.

[0027] The beneficial effects of this invention are as follows: (1) In terms of process and parameter control, the present invention adopts a dry mixing process with low-speed shearing, which only plays the function of uniform mixing and does not include the fiberization treatment of the adhesive, i.e., non-independent fiberization pretreatment. This avoids the fiber network damage caused by premature fiberization of the adhesive due to high-speed shearing. In the subsequent hot pressing process, the dry composite film formation of the adhesive is triggered in situ by precisely controlling process parameters such as temperature and pressure. This allows the polytetrafluoroethylene (PTFE) powder to fiberize and form a three-dimensional network structure and encapsulate the active material. This enables the fiber network construction and electrode film densification to proceed simultaneously, ensuring that PTFE is fully fiberized without being degraded due to excessive heating, thereby improving the bonding force of the electrode interface. Two dry process routes are adopted: electrostatic spraying and dry calendering. Electrostatic spraying controls the deposition thickness and uniformity of lead-based active material by setting parameters such as voltage and powder feeding rate, so as to achieve uniform and controllable deposition of dry powder, which is particularly suitable for the preparation of ultrathin electrodes. Dry calendering, on the other hand, is easy to form a dense and high-strength self-supporting film. By adjusting the powder feeding rate of electrostatic spraying or the pressure curve of dry calendering, the porosity of the electrode film can be gradient-distributed in the direction perpendicular to the current collector. The porosity is lower near the current collector to ensure interfacial bonding, and higher near the electrolyte to facilitate wetting and ion transport, thereby optimizing the electrolyte wetting and ion transport efficiency.

[0028] (2) In terms of raw material selection and pretreatment, this invention adopts a composite adhesive system, using PTFE powder as the main binder and utilizing its fibrous properties to construct a three-dimensional network. At the same time, it innovatively introduces surface-modified thermoplastic polyurethane (TPU) as a synergistic binder, which has excellent acid resistance and effectively copes with the acidic environment of lead-acid batteries and the volume changes during charging and discharging. The low glass transition temperature and excellent toughness of TPU improve the low tensile properties of PTFE, compensate for the brittleness of polyPTFE, and thus enhance the corrosion resistance and flexibility of the electrode, enabling it to cope with the acidic environment of lead-acid batteries and the volume changes during charging and discharging. The ability to change volume enhances cycle life and stability; surface treatments such as plasma etching or deposition of conductive carbon layers on stainless steel current collectors effectively increase their specific surface area and roughness, significantly improving their mechanical interlocking force and peel strength with the active material layer; and carbon coating or metal oxide coating on lead-based active materials forms a stable protective layer on their surface, effectively coping with the acidic environment of lead-acid batteries, preventing corrosion or passivation in strong acid environments, while improving their compatibility with the three-dimensional network of binders and alleviating the agglomeration tendency of high-density lead powder, thereby promoting uniform film formation.

[0029] (3) In terms of product performance, the lead-acid battery powder bonded thin film electrode prepared by the present invention has outstanding advantages such as short ion transport path, strong interfacial bonding force (peel strength ≥20N / m), porosity gradient distribution (20%-40%) to optimize electrolyte wetting, high rate performance (1C rate discharge capacity retention rate 90%) and long cycle life (capacity retention rate ≥85% after 600 cycles).

[0030] (4) The present invention adopts a pure dry preparation process, which completely eliminates solvents, making it environmentally friendly and energy-saving.

[0031] In summary, this invention has advantages such as environmentally friendly and energy-saving process, low electrode internal resistance, high utilization rate of active materials, strong interfacial bonding and good stability, and significantly improved battery rate performance and cycle life. It is especially suitable for the preparation of dry powder-bonded thin film electrodes for lead-acid batteries. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a graph showing the cycle capacity retention rate of the lead-acid battery in this invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1: Preparation of negative electrode based on electrostatic spraying A method for preparing a dry powder-bonded thin-film electrode, such as... Figure 1 As shown, it includes the following steps: Raw material preparation: Take lead powder, acetylene black, PTFE powder and TPU powder with a mass percentage (wt%) of 93:3:3:1; Dry mixing: Under argon protection, the above raw materials are mixed at 1500 rpm for 20 minutes using a shear mixer to obtain a mixed dry powder; Electrostatic spraying: The above-mentioned mixed dry powder is loaded into an electrostatic spraying equipment, a voltage of 40kV is applied, and the powder is sprayed onto a 304 stainless steel foil that has been plasma etched, with the film thickness controlled to be about 100μm. Hot pressing: The coated electrode sheet is hot pressed at 180°C and 30MPa for 2 minutes to bond PTFE+TPU adhesive fibers together with lead powder and other materials to form a composite film.

[0035] The negative electrode prepared by this method has a peel strength of 25 N / m and an active material utilization rate that is increased by about 20% (compared to traditional paste electrodes).

[0036] Example 2: Preparation of cathode material based on dry rolling A method for preparing a dry powder-bonded thin-film electrode, such as... Figure 1 As shown, it includes the following steps: Raw material preparation: Take lead oxide, carbon nanotubes, PTFE powder and TPU powder in a mass percentage (wt%) of 90:5:4:1; Dry mixing: Under argon protection, the above raw materials are mixed at 2000 rpm for 15 min using a shear mixer to obtain a mixed dry powder; Calendering film formation: The above mixed dry powder is directly calendered into an electrode film with a thickness of about 120 μm through a two-roll calender; Membrane lamination: The above electrode film and 316L stainless steel foil are hot-pressed at 170°C and 15MPa for 3 minutes to complete the lamination.

[0037] Example 3: Battery Assembly and Performance Testing Battery assembly: The negative electrode prepared in Example 1 and the positive electrode prepared in Example 2 are used together with an AGM separator to assemble a lead-acid battery.

[0038] Performance testing: Tests show that the battery retains 90% of its capacity at a 1C discharge rate and over 85% of its capacity after 600 cycles at a 0.2C rate. Figure 2 As shown.

[0039] Example 4: Preparation of Gradient Porosity Anode Based on Electrostatic Spraying Electrostatic spraying: A programmed powder feeding system is used, with the powder feeding rate linearly decreasing from an initial 10g / min to 2g / min within 60s.

[0040] The remaining steps are the same as in Example 1.

[0041] In this embodiment, the electrostatic spraying step achieves a gradual decrease in powder deposition density from the inside to the outside through gradient powder feeding.

[0042] Example 5: Preparation of Gradient Porosity Cathode Based on Dry Calendering Dry calendering: Using a calender with pressure gradient control, the pressure is linearly reduced from the initial 30MPa to 5MPa and completed in 3 calendering passes.

[0043] The remaining steps are the same as in Example 2.

[0044] In this embodiment, the dry calendering step achieves a gradual decrease in film compaction from the inside out by setting a pressure gradient.

[0045] Tests show that the gradient electrodes prepared in Examples 4 and 5 have a porosity of about 25% near the current collector and about 38% on the outer surface. Battery tests show that their rate performance is improved by about 15% compared to the non-gradient electrode, and their cycle life is also improved.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dry powder-bonded thin-film electrode, characterized in that, Includes the following steps: S1, Dry mixing: Lead-based active material, conductive agent and binder are mixed at low speed dry method to obtain mixed dry powder; S2, the mixed dry powder is applied to the surface of the current collector by electrostatic spraying or dry calendering to form an electrode film; S3, Hot pressing: Hot pressing is performed at 160~220℃ and 10~50MPa for 1~5min. During this process, the adhesive undergoes in-situ fibrosis, which extends and entangles with each other to form a three-dimensional network structure, thereby encapsulating and bonding the active material and conductive agent together. The mixed dry powder particles are also compacted to densify the electrode film.

2. The method for preparing a dry powder-bonded thin-film electrode according to claim 1, characterized in that, In step S1, the lead-based active material is modified by surface coating, and the coating layer is carbon or amorphous metal oxide with a coating layer thickness of 1~10 nm.

3. The method for preparing a dry powder-bonded thin-film electrode according to claim 1, characterized in that, In step S1, the adhesive comprises polytetrafluoroethylene and thermoplastic polyurethane, and the mass ratio of the two is 70~99:30~1.

4. The method for preparing a dry powder-bonded thin-film electrode according to claim 3, characterized in that, The thermoplastic polyurethane is a polyether type and has been surface modified with nano-silica.

5. The method for preparing a dry powder-bonded thin-film electrode according to claim 1, characterized in that, In step S1, a shear mixer is used for low-speed dry mixing, with a mixing speed of 1000~3000 rpm and a mixing time of 10~30 min.

6. The method for preparing a dry powder-bonded thin-film electrode according to claim 1, characterized in that, In step S2, the voltage for electrostatic spraying is 20~60kV, and the electrode film thickness is controlled to be 50~150μm by adjusting the voltage and powder feeding rate.

7. The method for preparing a dry powder-bonded thin-film electrode according to claim 1, characterized in that, In step S2, the powder feeding rate of electrostatic spraying is gradually reduced or the pressure of dry calendering is gradually reduced so that the porosity of the electrode film is gradually increased from the current collector side outward.

8. The method for preparing a dry powder-bonded thin film electrode according to claim 1, characterized in that, In step S2, the current collector is made of stainless steel foil and has undergone surface modification treatment such as roughening or conductiveing.

9. A dry-process powder-bonded thin-film electrode, characterized in that, It includes a stainless steel current collector and an electrode active material layer formed on the surface of the stainless steel current collector, wherein the peel strength between the electrode active material layer and the stainless steel current collector is ≥20 N / m, and the 1C capacity retention rate is ≥90%; The electrode active material layer is a porous thin film structure with an adjustable porosity in the range of 20-40%, and its porosity increases in a gradient from the stainless steel current collector side outwards.

10. A lead-acid battery, characterized in that, Its positive and / or negative electrodes adopt the dry powder bonded thin film electrode as described in claim 9, and the battery retains ≥85% capacity after 600 cycles at 0.2C rate.

Images