Battery diaphragm, preparation method thereof and secondary battery

Abstract

The invention relates to the technical field of battery diaphragms, in particular to a battery diaphragm, a preparation method thereof and a battery. The battery diaphragm comprises a base material and a coating on the surface of the base material, wherein the coating comprises a temperature-responsive component; wherein the temperature-responsive component comprises one or more of poly (N-alkyl acrylamide), poly (N-alkyl acrylate), poly (low polyethylene glycol) acrylate, polyvinyl ether and natural macromolecules. According to the invention, the continuous or discontinuous temperature-responsive coating is arranged to form the electrolyte storage bank, so that the stored electrolyte can be released under the action of temperature, the distance through which the electrolyte infiltrates is greatly shortened, the area near the coating material is rapidly infiltrated, the infiltrating of the roll core is accelerated, and a better infiltrating effect is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a battery separator and a preparation method thereof, and a battery. Background Art

[0002] Electrochemical energy storage devices, such as lithium-ion batteries and other secondary batteries, have the characteristics of high energy density, high output power, long cycle life, no memory effect, etc., and are widely used in 3C consumer electronics, power vehicles, large-scale energy storage and other fields. The diaphragm is a key component in the internal structure of the secondary battery. It has the function of conducting ions and blocking electrons, allowing ions to be transmitted between the positive and negative electrodes and blocking the direct contact between the positive and negative electrodes.

[0003] The wetting characteristics of the diaphragm and the electrolyte affect the processing and performance of the secondary battery. Poor wetting can easily lead to uneven lithium deposition or black spots on the battery interface, causing a decrease in battery capacity and other performance. The lithium deposition area may also cause battery safety problems in the later stages of the cycle.

[0004] At present, methods to improve the wettability of the diaphragm and electrolyte include introducing hydrophilic ceramic coatings and hydrophilic modification of the substrate surface. These methods are more effective for small-sized secondary batteries, but as the battery size increases, the effect of improving wettability decreases. During the battery charging process, the volume of the pole pieces expands, squeezing the electrolyte between the pole pieces out of the core and flowing around the core; during the battery discharging process, the squeezed electrolyte re-enters the core. As the battery size increases, the time required for the electrolyte to re-enter the core and fully infiltrate increases accordingly.

[0005] Based on the above problems, the present invention is proposed. Summary of the invention

[0006] In order to solve the above problems in the prior art, the present invention provides a battery separator and a preparation method thereof and a secondary battery, which can simply and efficiently achieve rapid infiltration of electrolyte, reduce the interface resistance of the battery, and further improve the electrochemical performance of the battery.

[0007] Based on this, the present invention has the following technical solutions: In a first aspect, the present invention provides a battery separator, comprising a substrate and a coating on the surface of the substrate, wherein the coating comprises a temperature-responsive component; wherein the temperature-responsive component comprises one or more of poly N-alkyl acrylamide, poly N-alkyl acrylate, poly (oligoethylene glycol) acrylate, polyethylene ether and natural macromolecules.

[0008] According to a battery separator provided by the present invention, the temperature responsive component includes one or more of poly (N-isopropylacrylamide), poly (N,N-dimethylaminoethyl methacrylate), poly (methacrylate oligoethylene glycol), poly (methyl vinyl ether) and hydroxybutyl chitosan.

[0009] According to a battery separator provided by the present invention, the coverage rate of the coating on the surface of the substrate on the substrate is 5-50%.

[0010] According to a battery separator provided by the present invention, the coating on the surface of the substrate also includes other components, and the other components include one or more of fluorine-containing polymers, polyacrylates and polyacrylonitrile and their homopolymers or copolymers; preferably, the other components include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate and polyacrylonitrile.

[0011] According to a battery separator provided by the present invention, the mass ratio of the temperature responsive component to the other components is (3-30): (70-97).

[0012] According to a battery separator provided by the present invention, the coating thickness on the surface of the substrate is 1 to 7 microns.

[0013] According to a battery separator provided by the present invention, the thickness of the substrate is 3 to 50 microns; the porosity is 25% to 65%; preferably, the substrate includes one of polyethylene film, polypropylene film, polyimide film, polyester film and non-woven fabric, and their composite films and ceramic coated films.

[0014] In a second aspect, the present invention provides a method for preparing the battery separator, comprising: mixing a temperature-responsive component, other components and water to obtain a mixed slurry; and coating the mixed slurry on a surface of a substrate to obtain the battery separator.

[0015] According to the preparation method of the battery separator provided by the present invention, the coating method includes gravure coating, micro-gravure coating, relief coating, array dot coating or rotary spraying; preferably, the coating amount is 0.6~1.2 g / m2.

[0016] In a third aspect, the present invention provides a secondary battery comprising a positive electrode, a negative electrode and the battery separator.

[0017] The battery separator and its preparation method and the secondary battery provided by the present invention form an electrolyte storage reservoir by setting a continuous or discontinuous temperature-responsive coating, which can release the stored electrolyte under the action of temperature, greatly shortening the distance that the electrolyte needs to pass through for infiltration, allowing the area near the coating material to be quickly infiltrated, accelerating the infiltration of the core, and achieving a better infiltration effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a schematic diagram of the discontinuous temperature responsive coating in Example 1 provided by the present invention.

[0020] Figure 2 This is a schematic diagram of the continuous temperature responsive coating in Example 10 provided by the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In a first aspect, the present invention provides a battery separator, comprising a substrate and a coating on the surface of the substrate, wherein the coating comprises a temperature-responsive component; wherein the temperature-responsive component comprises one or more of poly N-alkyl acrylamide, poly N-alkyl acrylate, poly (oligoethylene glycol) acrylate, polyethylene ether and natural macromolecules.

[0023] In the present invention, the temperature responsiveness of the temperature responsive component means that when the temperature rises due to battery operation, the coating undergoes a volume phase transition, and the electrolyte stored in the coating material is released due to the shrinkage of the particle volume, so that the electrolyte quickly reaches the area near the coating material, thereby accelerating the infiltration of the battery cell interface.

[0024] In the present invention, the function of the temperature-responsive component is to store and release electrolyte. When the battery temperature reaches above the response temperature, the electrolyte stored in the coating material is released due to the volume phase transition of the material. Specifically, the response temperature refers to the temperature at which the material begins to undergo a volume phase transition, and those skilled in the art can adjust it by selecting or controlling the proportion of the material. The response threshold of the temperature-responsive component is a temperature range of 25 to 60 degrees Celsius. When the battery is stored below the response threshold temperature, the excess electrolyte is stored in the coating material; when the battery generates heat during operation or the external temperature control causes the battery temperature to be higher than the response threshold temperature, the coating material shrinks and releases the electrolyte, allowing the battery interface to be quickly infiltrated, thereby improving the battery performance. At the same time, when stored at room temperature, the coating is in a highly swollen state, which is beneficial to suppress the self-discharge phenomenon of the battery and improve the room temperature storage performance of the battery.

[0025] According to a preferred embodiment provided by the present invention, the temperature responsive component includes one or more of poly (N-isopropylacrylamide), poly (N,N-dimethylaminoethyl methacrylate), poly (methacrylate oligoethylene glycol), poly (methyl vinyl ether) and hydroxybutyl chitosan.

[0026] In the present invention, the coating containing the temperature responsive component can be disposed on one side or both sides of the diaphragm base material, in a continuous or discontinuous morphology.

[0027] According to a preferred embodiment provided by the present invention, the coverage of the coating on the surface of the substrate on the substrate is 5-50%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0028] The present invention further finds that the battery performance can be further improved by controlling the coverage of the coating on the surface of the substrate to be within the above range.

[0029] According to a preferred embodiment provided by the present invention, the coating on the surface of the substrate also includes other components, and the other components include one or more of fluorine-containing polymers, polyacrylates and polyacrylonitrile and their homopolymers or copolymers; more preferably, the other components include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate and polyacrylonitrile.

[0030] According to a preferred embodiment provided by the present invention, the mass ratio of the temperature responsive component to the other components is (3-30):(70-97); further preferably, the mass ratio of the temperature responsive component to the other components is (15-25):(75-85).

[0031] In the present invention, if the content of the temperature-responsive component is too low, it is difficult to exert the temperature-responsive function, and the coating effect is weakened; if the content of the temperature-responsive component is too high, it is easy to cause the coating material to swell too much, store too much electrolyte, and affect the performance of the battery cell.

[0032] According to a preferred embodiment provided by the present invention, the coating thickness on the surface of the substrate is 1 to 7 microns, for example, 1 micron, 2 microns, 3 microns, 4 microns, 5 microns, 6 microns or 7 microns can be selected.

[0033] According to a preferred embodiment provided by the present invention, the thickness of the substrate is 3 to 50 microns; the porosity is 25% to 65%; more preferably, the substrate includes one of polyethylene film, polypropylene film, polyimide film, polyester film and non-woven fabric, as well as their composite films and ceramic coated films.

[0034] In a second aspect, the present invention provides a method for preparing the battery separator, comprising: mixing a temperature-responsive component, other components and water to obtain a mixed slurry; and coating the mixed slurry on a surface of a substrate to obtain the battery separator.

[0035] According to a preferred embodiment provided by the present invention, the coating method includes gravure coating, micro gravure coating, relief coating, array dot coating or rotary spray coating; preferably, the coating amount is 0.6-1.2 g / m2.

[0036] Furthermore, the single-sided coating amount is 0.6-0.7 g / m2, and the double-sided coating amount is 1.0-1.2 g / m2.

[0037] In a third aspect, the present invention provides a secondary battery comprising a positive electrode, a negative electrode and the battery separator.

[0038] Unless otherwise specified, the various raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0039] Examples and Comparative Examples

[0040] Example 1

[0041] This embodiment provides a battery separator, and its preparation method comprises the following steps (see the flow chart for details) Figure 1 ): Step 1: Mix the temperature responsive component 1, other components 2 and water, wherein the temperature responsive component 1 is poly (N-isopropylacrylamide), and the other component 2 is poly (vinylidene fluoride-hexafluoropropylene copolymer), prepare a coating slurry according to the mass ratio of component 1 to component 2 of 20:80, and set the response temperature to 40 degrees Celsius; Step 2: Provide a substrate of 9-micron polyethylene film with a porosity of 40%, and set the ceramic coating to single-sided 3-micron alumina; Step 3: Apply the slurry prepared in step 1 to the substrate by rotary spraying, apply it on one side of the ceramic, and set the coating amount to 0.6 g / m2 to prepare a non-continuous coated diaphragm.

[0042] This embodiment further provides a battery, the preparation method of which includes: Step 4: Provide positive and negative electrodes prepared by conventional methods. The positive and negative electrodes need to be matched, and provide conventionally used electrolytes. Step 5: Assemble the coated diaphragm, positive electrode, negative electrode, and electrolyte prepared in step 3 into an aluminum shell battery cell, and the matching electrolyte injection volume is 800g.

[0043] The preparation parameters of other embodiments and comparative examples are listed in Table 1, wherein the schematic diagram of the discontinuous temperature responsive coating in Example 1 is shown in Figure 1 , the schematic diagram of the continuous temperature responsive coating in Example 10 is shown in Figure 2 .

[0044] Table 1

[0045] Test example

[0046] 1. Liquid retention test

[0047] Test method: Let the prepared aluminum shell battery cells stand at room temperature for 72 hours, then let them stand at different temperatures (25 degrees Celsius / 35 degrees Celsius / 45 degrees Celsius / 55 degrees Celsius / 65 degrees Celsius) for 1 hour, and open the aluminum shell to fully pour out the free electrolyte under the corresponding temperature environment.

[0048] Liquid retention volume (g) = injection volume 800-free electrolyte volume.

[0049] The test results are shown in Table 2.

[0050] Table 2

[0051] It should be noted that, compared with the other embodiments, the coating coverage of Example 6 and Example 10 is 100%. Although the liquid retention amount can be guaranteed, too high a coverage will result in a lack of electrolyte wetting channels at the diaphragm and electrode interfaces, obstructed ion transmission, and uneven current density distribution, resulting in relatively poor electrical performance.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery separator, characterized in that: The invention comprises a substrate and a coating on the surface of the substrate, wherein the coating comprises a temperature responsive component; wherein the temperature responsive component comprises one or more of poly N-alkyl acrylamide, poly N-alkyl acrylate, poly (oligoethylene glycol) acrylate, polyvinyl ether and natural macromolecules.

2. The battery separator according to claim 1, characterized in that: The temperature responsive component comprises one or more of poly N-isopropylacrylamide, poly N,N-dimethylaminoethyl methacrylate, poly methacrylate oligoethylene glycol ester, polymethyl vinyl ether and hydroxybutyl chitosan.

3. The battery separator according to claim 1, characterized in that: The coverage of the coating on the surface of the substrate on the substrate is 5-50%.

4. The battery separator according to any one of claims 1 to 3, characterized in that: The coating on the surface of the substrate also includes other components, which include one or more of fluorine-containing polymers, polyacrylates and polyacrylonitrile and their homopolymers or copolymers; preferably, the other components include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate and polyacrylonitrile.

5. The battery separator according to claim 4, characterized in that: The mass ratio of the temperature responsive component to the other components is (3-30):(70-97).

6. The battery separator according to any one of claims 1 to 5, characterized in that: The coating thickness on the surface of the substrate is 1 to 7 microns.

7. The battery separator according to any one of claims 1 to 6, characterized in that: The thickness of the substrate is 3 to 50 microns; the porosity is 25% to 65%; preferably, the substrate includes one of polyethylene film, polypropylene film, polyimide film, polyester film and non-woven fabric, and their composite films and ceramic coating films.

8. The method for preparing a battery separator according to any one of claims 1 to 7, characterized in that: include: Mixing the temperature-responsive component, other components and water to obtain a mixed slurry; The mixed slurry is coated on the surface of a substrate to obtain the battery separator.

9. The method for preparing a battery separator according to claim 8, characterized in that: The coating method includes gravure coating, micro gravure coating, relief coating, array dot coating or rotary spray coating; preferably, the coating amount is 0.3-2.0 g / m2.

10. A secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode and a separator, wherein the separator is the battery separator according to any one of claims 1 to 7.

Images