A separator for alkaline batteries and a method for preparing and using the same

Abstract

This application relates to a separator for alkaline batteries, its preparation method, and its application, belonging to the field of electrochemical device technology. It includes a porous base membrane and a gel precursor layer coated on at least one surface of the porous base membrane. By introducing a phase separation initiator that can be triggered by a specific concentration of alkaline electrolyte, the gel precursor layer coated on the base membrane undergoes in-situ phase separation only after battery electrolyte injection. This integrates the most complex porous structure forming step into the battery assembly process, simplifying the separator's manufacturing process. More importantly, this in-situ phase separation process allows the polymer matrix to form a gel functional layer with a three-dimensional interconnected pore structure at the electrode interface under liquid-phase mass transfer and thermodynamic drive. This achieves molecular-level interpenetration and conformal fusion with the electrolyte and electrode surface microstructure, reducing solid-solid interface contact impedance and constructing continuous, uniform, and efficient ion transport channels, thereby improving the battery's discharge capacity and overall electrochemical performance.

Description

Technical Field

[0001] This application relates to the field of alkaline battery technology, specifically to a separator for alkaline batteries, its preparation method, and its application. Background Technology

[0002] Alkaline batteries, such as nickel-metal hydride and zinc-manganese batteries, are widely used in consumer electronics, energy storage, and power tools due to their high energy density, relatively low cost, and environmental friendliness. The separator, as a key internal component of the battery, functions primarily to isolate the positive and negative electrodes to prevent short circuits, while also providing ion transport channels. The structure and performance of the separator, especially its interfacial characteristics with the electrodes and electrolyte, directly affect the battery's internal resistance, rate performance, cycle life, and safety; therefore, it has always been a key focus of research and improvement in this field.

[0003] Currently, alkaline battery separators are mainly based on nonwoven fabrics (such as polyamide, polyethylene / polypropylene composite fibers) or microporous membranes (such as porous polyethylene membranes prepared by wet or dry processes). The production of these separators typically involves complex physical or chemical pore-forming processes, such as stretching, phase separation (using and subsequently removing pore-forming agents during manufacturing), or fiber carding / spinbonding, to pre-form a stable porous structure. Existing technologies primarily focus on improving the electrolyte affinity, chemical stability, and mechanical strength of the substrate. Common techniques include surface grafting modification of the base membrane, coating with hydrophilic polymer coatings, or composite inorganic ceramic particles. However, these pre-formed and structurally fixed separators have inherent limitations: First, their rigid porous structure makes it difficult to achieve sufficient microscopic adhesion with the electrode surface (especially the rough zinc anode or sintered nickel cathode), resulting in high interfacial contact resistance; second, the complex pre-pore forming process increases production costs and energy consumption; third, existing coatings are mostly physical coverings or simple wetting, which cannot form a dynamic interface that deeply interpenetrates and integrates with the electrode and electrolyte inside the battery, limiting further improvement in ion transport efficiency.

[0004] Therefore, it is of great significance to develop an alkaline battery separator that has a simple preparation process, can achieve excellent integration with the electrode interface, and improve the overall performance of the battery. Summary of the Invention

[0005] This application provides a separator for alkaline batteries, its preparation method, and its application. The alkaline battery separator has the advantages of simple preparation process, excellent integration with the electrode interface, and improved overall battery performance.

[0006] Firstly, the separator for alkaline batteries provided in this application adopts the following technical solution: A separator for alkaline batteries includes a porous base membrane and a gel precursor layer coated on at least one surface of the porous base membrane. The gel precursor layer includes a polymer matrix and a phase separation initiator. When the phase separation initiator comes into contact with an alkaline electrolyte with a concentration of 2-7M, it can induce phase separation in the polymer matrix, forming a functional layer with a three-dimensional interconnected pore structure in situ on the porous base film.

[0007] By employing the above technical solution, a gel precursor layer containing a polymer matrix and a phase separation initiator is set on a porous base membrane. The phase separation initiator triggers phase separation of the polymer matrix upon contact with the alkaline electrolyte, enabling the separator to form a functional layer with a three-dimensional interconnected pore structure in situ on the base membrane during the battery electrolyte injection stage. This design simplifies the manufacturing process because the formation of the porous structure is integrated into the battery activation process, eliminating the need for additional complex pre-pore forming treatment during separator production. Simultaneously, the in-situ formed three-dimensional interconnected pore structure achieves high integration with the electrolyte and electrode interfaces, reducing interfacial impedance and promoting uniform and efficient ion transport, ultimately improving the discharge capacity and overall electrochemical performance of the alkaline battery.

[0008] Optionally, the phase separation initiator is an alkaline-triggered anionic phase separation agent. In an alkaline electrolyte, the phase separation initiator can release polyvalent anions or high charge density anions through dissolution, reaction, or dissociation, thereby changing the local ionic environment and solvent properties and triggering polymer phase separation.

[0009] By employing the above technical solution, the core mechanism of phase separation initiator in alkaline environments was clarified and utilized. Through design, it is specifically activated and releases multivalent or high-charge-density anions only when the electrolyte is injected into the battery. These ions effectively alter the local ionic strength and solvation properties around the polymer, thereby precisely and reliably triggering liquid-solid phase separation in the polymer matrix. This controlled phase separation process allows for the in-situ formation of a polymer functional layer with an ideal three-dimensional interconnected pore structure on the separator base membrane. This structure not only improves the ionic conductivity and electrolyte retention of the separator but also, due to its simultaneous formation with the battery system, ensures the functional layer's adaptability to the electrolyte environment and good compatibility with the electrode interface. Ultimately, this enhances the overall rate performance, cycle stability, and lifespan of the alkaline battery.

[0010] Optionally, the phase separation initiator includes inorganic polybasic acids, monobasic or polybasic organic acids, and compounds that produce salts through esterification under alkaline conditions.

[0011] By employing the above-mentioned technical solution, when these initiators and polymer matrix are co-coated onto the base membrane and come into contact with the strongly alkaline electrolyte inside the battery, inorganic polybasic acids and organic acids will dissociate or neutralize, while esterification compounds will react to generate corresponding salts. These processes all locally and rapidly release polyvalent anions and alter the ionic environment. These anions, through salting-out effect and specific interactions, effectively disrupt the thermodynamic equilibrium of the polymer system, triggering a controllable phase separation process, thereby enabling the polymer matrix to be reconstructed in situ, forming a through-hole three-dimensional porous structure. This in-situ formed porous functional layer enhances the membrane's ability to wet and retain the electrolyte, providing a low-impedance continuous transport channel for hydroxide ions, thereby reducing the battery's internal resistance and enhancing its high-current discharge capability and rate performance. Simultaneously, this stable porous polymer structure also improves the membrane's mechanical stability and long-term durability, ultimately producing positive and beneficial effects on the energy output efficiency and cycle life of alkaline batteries.

[0012] Optionally, the mass ratio of polymer matrix to phase separation initiator in the gel precursor is 1:0.1-3.

[0013] By adopting the above technical solution, a sufficiently high concentration of phase separation initiator in the polymer matrix is ​​ensured, so that it can fully and controllably interact with a specific concentration of alkaline electrolyte during battery injection, reliably triggering the phase separation process of the polymer. At the same time, this upper limit of content avoids the problem of decreased stability of coating solution or low mechanical strength of precursor layer that may be caused by excessive initiator, ensuring the physical integrity and process feasibility of the separator during drying, storage and battery assembly.

[0014] Therefore, this preferred range is a key parameter for achieving the "electrolyte-triggered, in-situ formation of a uniform three-dimensional interconnected pore structure" of the separator. It balances the reliability of functional realization with the processability and stability of the precursor product, and ultimately provides an important guarantee for obtaining alkaline batteries with high interface integration and excellent ion transport performance.

[0015] Optionally, the polymer matrix includes one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyethylene oxide, and copolymers thereof.

[0016] By adopting the above technical solution, the polymers used as the matrix material of the gel precursor layer are selected to ensure that they can synergistically act with the phase separation initiator when in contact with alkaline electrolyte, effectively triggering the phase separation process. These polymers have excellent hydrophilicity and film-forming ability, which makes the gel precursor layer formed after coating uniform and stable, and undergoes rapid phase change after being wetted by electrolyte, thereby constructing a three-dimensional porous functional layer with regular structure and interconnected pores in situ. This not only enhances the wettability and interfacial fusion between the separator and the electrolyte, but also promotes the uniform transport of ions between electrodes, ultimately reducing the internal impedance of the battery and improving the discharge capacity and overall electrochemical performance.

[0017] Secondly, this application provides a method for preparing a separator for alkaline batteries, comprising the following steps: S1. Provide a porous base membrane; S2. Prepare a gel precursor coating solution containing polymer, phase separation initiator and solvent; S3. The gel precursor coating solution obtained in step S2 is uniformly coated onto the porous base membrane provided in step S1. After drying, a diaphragm with a gel precursor layer is obtained.

[0018] By adopting the above technical solution, the preparation of the membrane semi-finished product can be completed through conventional coating and drying processes, while the most complex and delicate porous functional layer forming process is transferred and integrated into the subsequent battery electrolyte injection and activation stages. This design greatly simplifies the production process, reduces reliance on complex pore-forming equipment and high-energy-consuming processes, and thus effectively reduces production costs. Simultaneously, since the final functional layer structure is formed in situ inside the battery, it can achieve full wetting and fusion with the electrolyte and electrode interfaces, laying a solid foundation for constructing a battery internal environment with lower impedance and more uniform ion transport, ultimately contributing to improved battery electrochemical performance.

[0019] Thirdly, the separator provided in this application for alkaline batteries is used in alkaline batteries including a positive electrode, a negative electrode, and an alkaline electrolyte.

[0020] By adopting the above technical solution, when the separator is applied in a battery system consisting of a positive electrode, a negative electrode, and an alkaline electrolyte of a specific concentration, the electrolyte will trigger in-situ phase separation of the gel precursor layer in the separator, thereby directly forming a functional layer with a three-dimensional interconnected pore structure at the electrode interface during the activation stage inside the battery. This process not only enables the separator to achieve molecular-level interfacial fusion with the electrode and electrolyte, reduces interfacial contact impedance, and optimizes the uniformity of ion transport, but also ultimately improves the discharge capacity and overall electrochemical performance of the alkaline battery containing the separator.

[0021] In summary, this application includes at least one of the following beneficial technical effects: By introducing a phase separation initiator that can be triggered by a specific concentration of alkaline electrolyte, the gel precursor layer coated on the base film undergoes in-situ phase separation only after the battery is injected with electrolyte. This integrates the most complex porous structure forming step into the battery assembly process, simplifying the manufacturing process of the separator itself. More importantly, this in-situ phase separation process enables the polymer matrix to form a gel functional layer with a three-dimensional interconnected pore structure at the electrode interface under the liquid phase mass transfer and thermodynamic drive. This achieves molecular-level interpenetration and conformal fusion with the electrolyte and the microstructure of the electrode surface, reduces the solid-solid interface contact impedance, and constructs a continuous, uniform, and efficient ion transport channel, thereby improving the battery's discharge capacity and overall electrochemical performance. Detailed Implementation

[0022] Example 1 A separator for alkaline batteries, the preparation method of which includes the following steps: S1. Preparation of gel precursor coating solution: Dissolve 10g of polyvinyl alcohol in 90g of deionized water and stir at 90℃ until completely dissolved to obtain a polymer solution. After cooling to 50℃, add 5g of sodium bicarbonate and stir until completely dissolved. S2. Separator preparation: Using commercially available vinylon nonwoven fabric as the base membrane, the gel precursor coating liquid obtained in step S1 is uniformly coated onto the surface of the base membrane using a wire bar coater. The membrane is then dried in a 60°C forced-air drying oven for 10 minutes to obtain a separator with a gel precursor layer, wherein the dried gel precursor layer accounts for 16% of the membrane mass.

[0023] Example 2 A separator for alkaline batteries differs from Example 1 in that polyvinyl alcohol is replaced with an equal amount of polyvinylpyrrolidone.

[0024] Example 3 A separator for alkaline batteries differs from Example 1 in that polyvinyl alcohol is replaced with an equal amount of polyacrylic acid.

[0025] Example 4 A separator for alkaline batteries differs from Example 1 in that polyvinyl alcohol is replaced with an equal amount of polyethylene oxide.

[0026] Example 5 A separator for alkaline batteries differs from Example 1 in that sodium bicarbonate is replaced with 10g of propylene carbonate.

[0027] Example 6 A separator for alkaline batteries differs from Example 1 in that sodium bicarbonate is replaced with 12g of citric acid.

[0028] Example 7 A separator for alkaline batteries differs from Example 1 in that the dried gel precursor layer accounts for 35% of the membrane mass, and the mass ratio of polymer matrix to phase separation initiator in the gel precursor is 1:0.8.

[0029] Example 8 A separator for alkaline batteries differs from Example 1 in that the dried gel precursor layer accounts for 60% of the membrane mass, and the mass ratio of polymer matrix to phase separation initiator in the gel precursor is 1:2.

[0030] Example 9 A separator for alkaline batteries differs from Example 1 in that it is a commercially available vinylon nonwoven separator without a gel precursor coating liquid and without any coating.

[0031] Comparative Example 1 A separator for alkaline batteries differs from Example 1 in that polyvinyl alcohol is replaced with an equal amount of polytetrafluoroethylene.

[0032] Comparative Example 2 A separator for alkaline batteries differs from that in Example 1 in that the dried gel precursor layer accounts for 5% of the membrane mass.

[0033] Comparative Example 3 A separator for alkaline batteries differs from Example 1 in that the dried gel precursor layer accounts for 70% of the membrane mass.

[0034] Detection example Referring to SJ / T 10171-2016 "General Test Methods for Basic Performance of Alkaline Battery Separators", the quantitative properties, thickness, longitudinal tensile strength, longitudinal alkali absorption rate, alkali absorption rate, and air permeability of the separator were tested. The quantitative calculation is performed by weighing a specified area of ​​diaphragm. Thickness was measured using a constant pressure thickness gauge; Longitudinal tensile strength was tested using an electronic tensile testing machine; The longitudinal alkali uptake rate was determined by recording the height of the 6M KOH electrolyte as it climbed longitudinally along the diaphragm within 3 minutes. The alkali absorption rate was determined by immersing the diaphragm in 6M KOH electrolyte for 30 minutes and measuring the percentage of electrolyte absorbed. Air permeability is measured using an air permeability meter and characterizes how easily air passes through the membrane; The opening voltage, internal resistance, and discharge time of the LR6 alkaline battery prepared with a separator were tested in accordance with GB / T 8897.2-2021 "Primary Cells - Part 2: Dimensional and Electrical Performance Requirements" and corresponding test methods. Among them, the open-circuit voltage is measured using a high internal resistance voltmeter after the battery has been aged for 24 hours. The internal resistance was measured by using the AC impedance method to determine the total internal resistance of the battery. The discharge duration was determined by continuously discharging at a constant resistance of 3.9Ω under an environment of (20±2)℃ until the termination voltage of 0.9V, and the total discharge time was recorded. The specific test results are shown in Tables 1 and 2.

[0035] Table 1: Comparison of parameters for different diaphragms

[0036] Table 2: Performance Comparison of LR6 Batteries Prepared with Different Separators

[0037] The performance test data in Tables 1 and 2 of Examples 1-4 and Example 9 (blank control) show that, although the initial permeability of the separator coated with gel precursor layers containing different polymer matrices and phase separation initiators was lower than that of the pure base membrane (Example 9), it exhibited lower internal resistance and longer discharge time in battery applications. This indicates that after contact with alkaline electrolyte, the gel precursor layer successfully underwent in-situ phase separation, forming an excellent three-dimensional interconnected pore structure. This not only retained sufficient alkali absorption but also greatly improved the interfacial contact between the separator and the electrode, reducing interfacial impedance. Among them, Examples 1 (PVA) and 3 (PAA) showed better swelling and liquid retention capabilities in alkaline solutions due to the abundant hydroxyl and carboxyl groups on their molecular chains, resulting in particularly outstanding discharge performance.

[0038] A comparison of the data from Example 1 and Comparative Example 1 shows that replacing the polymer matrix with highly hydrophobic PTFE significantly reduced the longitudinal alkali absorption rate and alkali absorption percentage of the membrane, while greatly increasing the internal resistance and shortening the discharge time. This confirms that having only a coating without an effective hydrophilic matrix and a phase separation mechanism that can be triggered by alkali (PTFE does not undergo this reaction) will lead to membrane pore blockage and poor hydrophilicity, hindering ion transport.

[0039] Comparative analysis of Examples 1, 5, and 6 shows that whether using inorganic salts (sodium bicarbonate) that dissociate in alkaline solution, organic compounds (propylene carbonate) that produce salts through esterification, or organic acids (citric acid), all can effectively trigger the phase separation mechanism and improve battery performance. Example 5, due to the time required for the esterification reaction, has slightly lower permeability and slightly higher internal resistance, but it is still superior to the uncoated blank control, demonstrating the universality of this mechanism.

[0040] Analysis of the data in Tables 1 and 2 of Examples 1, 7, and 8 and Comparative Examples 2 and 3 shows that there is an optimal window for the coating amount of the gel precursor layer and the ratio of the inducer.

[0041] Although the coatings in Examples 8 and 7 were thicker than those in Example 1, the increased initiator ratio resulted in extremely high in-situ porosity (manifested as extremely high alkali absorption), leading to very low internal resistance (68.7 mΩ). However, the excessively high degree of phase separation and the thinner substrate ratio (only 36.9% in Example 8) prevented the maximization of discharge time (367.5 min vs. 410.2 min in Example 1). This may be because while excessive porosity facilitates ion transport, it may also exacerbate zincate penetration, affecting the battery's self-discharge or reaction efficiency, or it may be due to insufficient polymer backbone leading to slightly weaker mechanical integrity.

[0042] In contrast, Comparative Example 2 had too little coating (5%), which had a negligible effect on improving the interface, and its internal resistance and discharge performance were only slightly better than the blank group (Example 9).

[0043] In contrast, in Comparative Example 3, the coating amount was too high (70%), resulting in extremely low overall air permeability of the separator (30 L / cm² / s). Furthermore, the excessively thick gel layer may have expanded excessively within the limited battery space, compressing the electrolyte channels and causing a sharp increase in internal resistance (95.1 mΩ), which seriously affected the discharge performance.

[0044] In summary, the gel precursor layer provided in this application, containing an appropriate amount of polymer matrix and a specific ratio of phase separation initiator, can form a porous functional layer with excellent structure in situ after battery electrolyte injection. This structure, while ensuring a certain level of mechanical strength, achieves high alkali absorption rate, low internal resistance, and excellent electrode interface fusion, thereby significantly improving the discharge capacity of alkaline batteries. The parameter ratios in Example 1 exhibit the best overall performance balance under the test conditions.

[0045] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A separator for alkaline batteries, characterized in that, It includes a porous base membrane and a gel precursor layer coated on at least one surface of the porous base membrane; The gel precursor layer includes a polymer matrix, a phase separation initiator, and a solvent. When the phase separation initiator comes into contact with an alkaline electrolyte with a concentration of 2-7M, it can induce phase separation in the polymer matrix, forming a functional layer with a three-dimensional interconnected pore structure in situ on the porous base film.

2. The separator for an alkaline battery according to claim 1, characterized in that, The phase separation initiator is an alkaline-triggered anionic phase separation agent. In an alkaline electrolyte, the phase separation initiator can release polyvalent anions or high charge density anions through dissolution, reaction, or dissociation, thereby changing the local ionic environment and solvent properties and triggering polymer phase separation.

3. The separator for an alkaline battery according to claim 2, characterized in that, The phase separation initiator includes inorganic polybasic acids, monobasic or polybasic organic acids, and compounds that produce salts through esterification under alkaline conditions.

4. The separator for an alkaline battery according to claim 1, characterized in that, The mass ratio of polymer matrix to phase separation initiator in the gel precursor is 1:0.1-3.

5. A separator for an alkaline battery according to claim 1, characterized in that, The polymer matrix includes one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyethylene oxide, and their copolymers.

6. A method for preparing a separator for an alkaline battery according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Provide a porous base membrane; S2. Prepare a gel precursor coating solution containing polymer, phase separation initiator and solvent; S3. The gel precursor coating solution obtained in step S2 is uniformly coated onto the porous base membrane provided in step S1. After drying, a diaphragm with a gel precursor layer is obtained.

7. The application of a separator for alkaline batteries according to any one of claims 1-5, characterized in that, It is used in alkaline batteries, which include a positive electrode, a negative electrode, and an alkaline electrolyte.

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