Method of manufacturing an electrochemical cell for separating electrodes with a separator and device therefor

Abstract

A method of preparing an electrochemical cell having a polymer separator for separating electrodes in the electrochemical cell is disclosed. The method includes providing a cathode, a polymer separator, and an anode. For the polymer separator, the polymer separator is irradiation modified by at least one irradiation cycle at a radiation dose ranging from 50 to 200 kGy by an energy beam to achieve cross-linking in the polymer separator, and the polymer separator is maintained at a temperature ranging from 30 to 70 °C, followed by compressing the polymer separator between the cathode and the anode, and finally providing an electrolyte to form the electrochemical cell.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of electrochemical cell technology. In particular, the present invention relates to a modified separator for separating electrodes in an electrochemical cell. BACKGROUND

[0002] Lithium ion batteries are commonly used in various electronic devices such as computers, mobile phones and electric vehicles. In addition to the existing applications, due to the high energy density, stable cycle performance and light weight characteristics of lithium ion batteries, people also consider using them in wearable electronic devices, therefore, as the increasing demand of battery capacity load from different practical applications, the demand of meeting the safety standards of lithium ion batteries has become a challenge, in order to prepare safe lithium ion batteries, there is an urgent need for a thermally stable separator for separating electrodes in an electrochemical cell.

[0003] Chinese patent CN103421208 discloses a preparation method of cross-linked polyethylene porous separator, by immersing the polyethylene porous separator in a volatile solution containing initiator and cross-linking agent, the polyethylene porous separator absorbs the initiator and cross-linking agent, then irradiation is carried out to make the initiator and cross-linking agent in it cross-linking reaction, so that the polyethylene porous separator is not easy to shrink at high temperature.

[0004] Chinese patent CN104882581A discloses a lithium ion battery separator and its preparation method, the preparation method is characterized in that the separator is washed in a siloxane solution containing ethylene and a polymerization inhibitor, and a grafting reaction between the cross-linking agent and the polyethylene separator is carried out by irradiation. Korean patent KR102073852B1 discloses a silane grafted polyolefin solution that facilitates cross-linking reaction, the solution includes polyolefin with a weight average molecular weight of 200000 or more, diluent, alkoxyl-containing vinyl silane and initiator. CN104882581A and KR102073852 use chemicals to promote cross-linking reaction, however, these treatments can only be carried out during the extrusion of the separator, and cannot be applied to the separator that has been set up and made. SUMMARY

[0005] This section is intended to summarize some aspects of the embodiments of the present invention and briefly introduce some other embodiments. In this section, as well as in the abstract and title of the present application, simplification or omission can be made to avoid obscuring the purpose of this section, abstract and title, and such simplification or omission is not intended to limit the scope of the present invention.

[0006] The purpose of the present invention is to overcome the above-mentioned related problems of the actual processing method for setting up and making the separator for the electrodes of the electrochemical cell by initiating the cross-linking reaction.

[0007] Accordingly, one aspect of the present application provides a method of making an electrochemical cell having a separator for separating electrodes in the electrochemical cell, the method comprising providing a cathode and providing a polymeric separator, subjecting the polymeric separator to at least one irradiation cycle with an energy beam in a range of 50 to 200 kGy of radiation dose, causing crosslinking in the polymeric separator, and then maintaining the polymeric separator at a temperature of 30 to 70 °C, followed by providing an anode, compressing the polymeric separator between the cathode and the anode, and finally providing an electrolyte to form the electrochemical cell.

[0008] In another embodiment of the present application, the polymeric separator has a gel content of the crosslinked polymeric separator of 30% to 90% after the at least one irradiation cycle of the polymeric separator with the energy beam.

[0009] In another embodiment of the present application, the polymeric separator comprises polypropylene, polyethylene, polyvinylidene fluoride, polyimide, polyacrylonitrile, or a combination thereof.

[0010] In another embodiment of the present application, the polymeric separator has a thickness in a range of 3 to 30 pm after the compressing the polymeric separator between the cathode and the anode.

[0011] In another embodiment of the present application, the making the polymeric separator further comprises applying a polymeric adhesive on opposite sides of the polymeric separator and adding a plurality of ceramic particles in the polymeric adhesive.

[0012] In another embodiment of the present application, the ceramic particles in the polymeric adhesive are selected from CaO nanoparticles, MgO nanoparticles, AI2O3 nanoparticles, B2O3 nanoparticles, SiO2 nanoparticles, ZrO2 nanoparticles, SnO2 nanoparticles, nanoclay, or a combination thereof.

[0013] In another embodiment of the present application, the polymeric adhesive comprises silane, acrylate, epoxy, polyurethane, polyolefin, ether, or a combination thereof.

[0014] In another embodiment of the present application, the at least one irradiation cycle of the polymeric separator with the energy beam further comprises a first irradiation of the polymeric separator for a first duration at a first radiation dose and a second irradiation for a second duration at a second radiation dose, wherein the first radiation dose is different from the second radiation dose and the first duration is different from the second duration.

[0015] In another embodiment of the present application, the making the polymeric separator further comprises making the polymeric separator by wet or dry extrusion, electrospinning, melt spinning, or a combination thereof.

[0016] In another embodiment of the present application, at least one irradiation cycle is performed on the polymer separator with an electron beam.

[0017] In another embodiment of the present application, at least one irradiation cycle is performed on the polymer separator with a gamma ray.

[0018] Another aspect of the present application provides an electrochemical cell comprising a cathode, an anode, an irradiated polymer separator having a coating, and an electrolyte, wherein the coating comprises a polymer binder having ceramic particles, and the irradiated polymer separator has cross-linked chemical bonds, however, the irradiated polymer separator is free of cross-linking agents or initiators, and the irradiated polymer separator has a shrinkage of less than 30% at 140°C.

[0019] In another embodiment of the present application, the irradiated polymer separator comprises polypropylene, polyethylene, polyvinylidene fluoride, polyimide, polyacrylonitrile, or a combination thereof.

[0020] In another embodiment of the present application, the irradiated polymer separator has a gel content in the range of 30% to 90%.

[0021] In another embodiment of the present application, the irradiated polymer separator has a thickness in the range of 3 to 30 μιη.

[0022] In another embodiment of the present application, the ceramic particles are selected from CaO nanoparticles, MgO nanoparticles, AI2O3 nanoparticles, B2O3 nanoparticles, SiO2 nanoparticles, ZrO2 nanoparticles, SnO2 nanoparticles, nanoclay, or a combination thereof.

[0023] In another embodiment of the present application, the polymer binder is selected from silane, acrylate, epoxy, polyurethane, polyolefin, ether, and a combination thereof. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the description of the embodiments. Obviously, the following drawing description is only some of the embodiments of the present application, and the skilled in the art can obtain other drawings according to the content of the embodiments of the present application without inventive operations:

[0025] Figures 1A to IE A schematic diagram of a method for preparing an electrochemical cell having a polymer separator for separating electrodes according to an embodiment of the present application is shown;

[0026] Figure 2 A schematic diagram of Figure IEEnlarged view of the middle region A showing a representative cross-linking structure of the polymer separator used to separate the electrodes of the electrochemical cell in the embodiments of the present application;

[0027] Figures 3A to 3E A schematic diagram of a method of making an electrochemical cell using a polymer binder with ceramic particles and a polymer separator is shown;

[0028] Figure 4 A schematic diagram of a method of making an electrochemical cell using a polymer binder with ceramic particles and a polymer separator is shown; Figure 3C Enlarged view of the middle region B showing the bonding relationship between the irradiated polymer separators;

[0029] Figure 5 A differential scanning calorimetry analysis plot of Sample 1 to Sample 4 and Comparative Sample 1 is shown;

[0030] Figures 6A to 6E A scanning electron microscope image of Sample 5 to Sample 8 and Comparative Sample 2 is shown, respectively;

[0031] Figures 7A to 7E A scanning electron microscope image of Sample 5 to Sample 8 and Comparative Sample 2 after heat treatment at 140°C for 1 hour is shown, respectively;

[0032] Figure 8A A schematic diagram of a hot needle penetration test of the polymer separator is shown; 8B

[0033] A schematic diagram of a hot needle penetration test of the polymer separator is shown; Figure 9A 9B A schematic diagram of a hot needle penetration test of the polymer separator is shown; and

[0034] Figures 10A to 10C A schematic diagram of a hot needle penetration test of the polymer separator is shown. DETAILED DESCRIPTION

[0035] Objects, features and advantages of the present application are further explained by the following detailed description in conjunction with the related drawings.

[0036] In the following description, for purposes of providing a thorough understanding of the present application, numerous specific details are set forth, however, it will be understood by one of ordinary skill in the art that the present application can be practiced without the specific details and that the present application should not be construed as being limited thereto.

[0037] The present application provides a method of making an electrochemical cell using a polymer separator to separate the electrodes. Referring to Figure 1A A cathode 110 is shown, wherein the cathode is an alkali metal salt, a transition metal salt and complexes thereof, and next, referring to Figure IB ​polymer separator 120, which is in a planar shape and has at least two flat surfaces opposite to each other, can be made of polypropylene, polyethylene, polyvinylidene fluoride, polyimide, polyacrylonitrile, or a combination thereof, and can be prepared by wet or dry extrusion, electrospinning, melt spinning, or a combination thereof.

[0038] Referring to Figure 1C The polymer separator 120 is irradiation-modified by irradiating an energy beam 1100 onto the polymer separator 120; in one embodiment, the energy beam 1100 is an electron beam; in another embodiment, the energy beam 1100 is a gamma ray. The irradiation dose of the energy beam ranges between 50 and 200 kGy, the duration of irradiation can be between 1 hour to 20 hours or 1 hour to 4 hours, and the irradiation ambient temperature must be maintained between 40 and 100 °C.

[0039] At high irradiation dose, for example, higher than 80 kGy, high temperature can be generated within the separator, and the temperature of the polymer separator can increase beyond the shrinkage threshold or melting point, therefore, longer irradiation can be performed by dispersing the irradiation to prevent thermal damage at high irradiation dose, for example, if the temperature exceeds 120 °C, the polymer separator can significantly shrink. In one embodiment, irradiation is performed for more than one cycle, for example, the first irradiation is performed at 50 kGy for 1 hour, maintaining the temperature of the polymer separator between 30 and 50 °C, and the second irradiation is performed at 100 kGy for 2 hours, maintaining the temperature of the polymer separator between 30 and 70 °C. It should be understood that different combinations of irradiation dose, duration, and temperature within the ranges provided are within the scope of the present application.

[0040] Referring to Figure 2 An enlarged view of the area A is shown. Figure 1C Figure 2 A representative schematic view of the irradiated polymer separator 120’ is shown, showing the bonding relationship between the polymer separator 120’. After irradiation by the energy beam 1100, the free radicals of the polymer separator are excited, and crosslinking reactions occur within the irradiated polymer separator 120’, forming crosslinking chemical bonds 120A.

[0041] ​The degree of cross-linking in the polymer separator 120’ was evaluated by a standard method of gel content (insoluble ratio), the gel content data results of the irradiated polymer separator 120’ were obtained according to the standard of ASTM D-2765, in brief, about 0.3 grams of the irradiated polymer separator 120’ was cut into small pieces and placed in a pre-weighed stainless steel gauze, a Soxhlet extraction cycle was performed at 150 °C for 20 hours with p-xylene as the solvent, and 0.5 weight percent (wt%) of antioxidant 1010 (Irganox 1010) was used to prevent the degradation of the polymer separator 120’ during the extraction process, after the extraction cycle, the sample was washed with acetone and vacuum dried to a constant weight, the gel content (gel ratio) was calculated as a percentage of the final weight of the polymer to its initial weight, the results showed that the irradiated polymer separator 120’ had a gel content (gel ratio) in the range of 30% to 90%.

[0042] Referring to Figure ID , the anode 150 is shown, wherein the anode 150 can be made of a graphene-based composite or lithium metal. Referring to Figure IE , the irradiated polymer separator 120’, the cathode 110 and the anode 150 were compressed together, wherein the irradiated polymer separator 120’ was between the cathode 110 and the anode 150, after compression, the irradiated polymer separator 120’ had a thickness in the range of 3 to 30 pm, subsequently, an electrolyte (not shown) was given, at this point, the electrochemical cell 10 prepared according to the embodiments of the present application was completed, the prepared separator had a shrinkage of less than 30% at 140 °C. In one embodiment, the shrinkage of the irradiated polymer separator 120’ at 140 °C was less than 25%.

[0043] In one embodiment, a polymer binder with ceramic particles was used simultaneously with the polymer separator. Referring to Figure 3A , the cathode 110 is shown, wherein the cathode is an alkali metal salt, a transition metal salt and complexes thereof. Next, referring to Figure 3B , the polymer separator 122 is shown, wherein the polymer separator 122 is in a planar shape and has at least two flat surfaces opposite to each other, the polymer separator 122 can be made of polypropylene, polyethylene, polyvinylidene fluoride, polyimide, polyacrylonitrile or a combination thereof, and the polymer separator can be prepared by wet or dry extrusion, electrospinning, melt spinning or a combination thereof. For the sake of clarity, the cathode 110 is not shown in Figures 3B to 3Dpolymer separator 122, and the polymer binder 130 can be made of silane, acrylate, epoxy, polyurethane, polyolefin, ether, or a combination thereof, wherein the polymer binder 130 has a plurality of ceramic particles 140 in it, the ceramic particles 140 are disposed in the polymer binder 130 by spraying, dipping, doctor blading, pad dry-cure coating, or wiping, wherein the ceramic particles 140 can be made of CaO nanoparticles, MgO nanoparticles, AI2O3 nanoparticles, B2O3 nanoparticles, SiO2nanoparticles, ZrO2nanoparticles, SnO2nanoparticles, nanoclay, or a combination thereof, and the size of the individual ceramic particles 140 is between 10 and 100 nm or between 10 and 50 nm. In one embodiment, the ceramic particles 140 with a particle size between 10 nm and 50 nm can be more tightly bound to the surface of the polymer separator 122, and the resulting electrochemical cell has a thinner profile associated with a higher thermal resistance.

[0044] Referring to Figure 3C , there is shown irradiating the polymer separator 122’ with the energy beam 1100. The irradiation can be performed in more than one cycle of radiation at different combinations of radiation dose and duration, as previously described.

[0045] Referring to Figure 4 , there is shown an enlarged view of the region B in Figure 3C . Figure 4 is a representative schematic diagram showing the bonding relationship between the irradiated polymer separator 122’, the cross-linking reaction occurs within the irradiated polymer separator 122’ after the irradiation by the energy beam 1100 to form the cross-linking chemical bonds 120A, and the ceramic particles 140 are connected to the polymer separator 122’ through the polymer binder bonds 130A, wherein the irradiated polymer separator 122’ has a gel content (gel fraction) in the range of 30% to 90%.

[0046] Referring to Figure 3D , there is shown the anode 150, wherein the anode 150 can be made of graphene-based composite or lithium metal. Referring to Figure 3EThe irradiated polymer separator 122' is placed between the cathode 110 and the anode 150 and compressed together, and after compression, the combined thickness of the irradiated polymer separator 122', the polymer binder 130 and the ceramic particles 140 is in the range of 3 to 30 μιη. Subsequently, an electrolyte (not shown) is applied, and at this point, the electrochemical cell 20 according to the embodiment of the present application is complete, and the shrinkage of the formed separator at 140°C is less than 30%. In another embodiment, the shrinkage of the irradiated polymer separator 120' at 140°C is less than 25%.

[0047] Referring to Figure 5 , a differential scanning calorimetry graph is shown, and samples 1 to 4 are respectively made of pure polyethylene with a size of 1.5 to 3 mg, and are respectively irradiated polymer separators treated by passing through different radiation doses of 50 kGy, 100 kGy, 150 kGy and 200 kGy, wherein comparative sample 1 represents a commercially available polymer separator, and the equilibrium temperature of the test curve is 25°C, and the temperature is raised to 200°C at a rate of 10°C / min, and the melting point and enthalpy (ΔH) of the sample are shown in Table 1.

[0048] Table 1

[0049] Melting point (°C) Enthalpy of fusion (J / g) Sample 1 139.71 177.0 Sample 2 138.75 179.2 Sample 3 137.10 240.0 Sample 4 135.95 212.7 Comparative Sample 1 140.82 203.3

[0050] As shown in Figure 5 , compared with the commercially available 1, the melting curves of samples 1 to 4 are more sharp, in other words, samples 1 to 4 exhibit faster phase change, and in Table 1, samples 3 and 4 have higher enthalpy compared with the commercially available polymer separator, which indicates that the heat capacity of samples 3 and 4 is higher, therefore, samples 3 and 4 treated by 150 kGy and 200 kGy respectively have higher thermal stability, and have a tendency to shift the melting curve from a higher temperature to a lower temperature. More specifically, the melting point of sample commercially available 1 is 140.82°C, and the melting point gradually decreases from sample 1 to sample 4, and thus it can be known that the radiation dose and the melting point are negatively correlated, and when the radiation dose is higher, for example, the melting point of sample 4 treated by passing through 200 kGy is the lowest among the five samples.

[0051] As shown in Figures 6A to 6E , scanning electron microscope analysis images of irradiated polymer separator samples 5 to 8 and comparative sample 2 are respectively shown, and the analysis results show that samples 5 to 8 (as shown in Figures 6A to 6D respectively) after irradiation have similar morphologies to comparative sample 2 (as shown in Figure 6E ), and the irradiation treatment does not cause morphological changes in the polymer separator.

[0052] Referring to Figures 7A to 7E, respectively, showing SEM analysis of sample 5 to sample 8 and comparative sample 2 after heat treatment at 140°C for 1 hour, sample 5 to sample 8 were treated with different radiation doses of 50 kGy, 100 kGy, 150 kGy and 200 kGy, respectively. See Figure 7E , comparative sample 2 without irradiation showed considerable holes and fragmentation after heat treatment, indicating that the polymer separator without irradiation treatment exhibited high shrinkage; see Figures 7A to 7D , in the irradiated polymer separator samples 5 to sample 8, after heat treatment, had relatively smooth surfaces and no holes were observed, that is, the irradiated polymer separator had high heat resistance and low shrinkage.

[0053] Heat shrinkage test

[0054] Samples 5 to sample 8, comparative sample 1 and comparative sample 2 were subjected to the following heat shrinkage test to simulate the situation of the separator of the electrode in the electrochemical cell at high temperature. Step 1, the anode was wrapped with a piece of separator and put into a pouch; Step 2, the pouch was dried at 90°C; Step 3, the dried pouch was placed in a glove box; Step 4, the anode with the separator was immersed in electrolyte for 24 hours; Step 5, the anode and the separator (in Al / cPP (cast polypropylene)) were vacuum sealed in a sealed bag; Step 6, the pouch was heated at 140°C (±3°C) for 1 hour; Step 7, the sealed bag was opened to check the status of the anode and the separator.

[0055] The shrinkage rate shown in Table 3 was obtained according to the following equation:

[0056]

[0057] A i is the initial coverage area of the separator, A f is the final coverage area of the separator, the results are shown in Table 3.

[0058] Table 3

[0059] Sample 5 Sample 6 Sample 7 Sample 8 Comparative Sample 1 Comparative Sample 2 Shrinkage 20％ 20％ 10％ 10％ 50％ 50％

[0060] The shrinkage rate of sample 5 to sample 8 was lower than that of comparative sample 1 and comparative sample 2, in addition, due to high shrinkage, the anode of comparative sample 1 and comparative sample 2 showed large area exposure, and the electrochemical cell stopped working, while due to the high heat resistance and low shrinkage of the irradiated separator, especially at high working temperature, sample 5 to sample 8 still maintained the function.

[0061] The melting point of the polymeric separator was between 130 and 145 °C. In the direction perpendicular to the film extrusion, the unirradiated polymeric separator showed a maximum shrinkage of -59% when the temperature was raised to about 150 °C; the irradiated polymeric separator treated with 50 kGy of electron beam or gamma rays showed a reduced shrinkage of -56%; the irradiated polymeric separator treated with 100 kGy of electron beam or gamma rays showed a further reduced shrinkage of about -49%; the irradiated polymeric separator treated with 150 kGy of electron beam or gamma rays showed the lowest shrinkage, which was reduced to a maximum of -40%.

[0062] In the direction perpendicular to the film extrusion, the unirradiated polymeric separator showed a shrinkage of -70% when the temperature was raised to about 150 °C; the irradiated polymeric separator treated with 100 kGy of electron beam or gamma rays showed a reduced shrinkage of -66%; the irradiated polymeric separator treated with 150 kGy of electron beam or gamma rays showed a reduced shrinkage of -60%.

[0063] Hot needle test

[0064] A hot needle test was performed to study the heat resistance of the irradiated polymeric separator. According to the embodiments of the present application, the irradiated polyethylene separator sample 9 was prepared using a radiation dose of 150 kGy of electron beam / gamma rays, while the comparative sample 3 was an unirradiated polyethylene separator, all samples were intact before the hot needle test, during the test, the sample was placed under a hot iron needle with a diameter of 5.5 mm, when the hot iron needle contacted the sample, the diameter of the hole appeared on the sample was recorded, the morphological observation results were illustrated in the form of a cartoon.

[0065] Referring to Figure 8A and 8B , the hot needle test of the comparative sample 3 and the sample 9 was performed at 186 °C, as Figure 8A , the unprocessed polymeric separator (comparative sample 3) showed a visible melting collapse 810 after contacting the hot iron needle at 186 °C; as Figure 8B , the sample 9 showed a hole 850 on the sample 9 after contacting the hot iron needle at 186 °C, and a thin and translucent irradiated polymeric separator ring was observed. In other words, the irradiated polymeric separator 860 of the sample 9 maintained its shape and had higher heat resistance, and protected its adjacent components by blocking heat transfer.

[0066] Referring to Figure 9A and 9B , the hot needle test of the comparative sample 3 and the sample 9 was performed at 320 °C (the temperature of the iron needle). As Figure 9A , the comparative sample 3 showed a hole 910 and a visible crimping stripe after contacting the hot iron needle at 320 °C; as Figure 9BAfter contact with the hot iron needle at 320 °C, holes 950 appeared on sample 9 and a thin and translucent irradiated polymer separator ring was observed. The irradiated polymer separator ring 960 of sample 9 showed stronger heat resistance compared to the untreated comparative sample 3.

[0067] Referring to Figures 10A to 10C , showing the results of hot needle test of the separator under different irradiation conditions, in which the separators were all contacted with a hot iron needle at 320 °C for 10 seconds. Figure 10A showing the irradiated separator treated with a gamma ray radiation dose of 100 kGy, holes 1010 appeared, and small curls at the edge of the irradiated separator, the holes 1010 still maintained their shape and had negligible phase change; Figure 10B showing the irradiated separator treated with a gamma ray radiation dose of 150 kGy, holes 1020 appeared, which were smaller in diameter than the holes 1010, and a ring 1030 became thinner and more transparent around the holes 1020, the translucent appearance indicated that the irradiated polymer separator experienced a smaller degree of melting, these results showed that the irradiated separator can effectively protect its constituent components from heat damage and only undergo a slight phase change. Figure 10C showing the results of hot needle test of the conventional polymer separator without irradiation, it can be observed that there is obvious heat damage on the polymer separator, including melting and curling.

[0068] As used herein, the terms “approximately,” “substantially,” “essentially,” and “about” are used to describe and account for small variations. When used in combination with an event or circumstance, the term can refer to the event or circumstance exactly occurring, as well as the event or circumstance approximately occurring. The term “about” as used herein with respect to a particular value or range generally means a range of ±10%, ±5%, ±1%, or ±0.5% of the particular value or range, ranges can be expressed herein from one endpoint to another endpoint or between two endpoints, unless otherwise indicated, all ranges disclosed in the present disclosure include the endpoints. The term “substantially co-planar” can refer to two surfaces positioned within a few micrometers (pm) of one another along the same plane, e.g., within 10 pm, within 5 pm, within 1 pm, or within 0.5 pm of one another along the same plane. When reciting to “substantially” the same numerical value or characteristic, the term can refer to a value within ±10%, ±5%, ±1%, or ±0.5% of the average of that value.

Claims

1. A method of preparing an electrochemical cell having a polymeric separator for separating electrodes in the electrochemical cell, characterized by, The method comprises: providing a cathode; providing a polymer separator; subjecting the polymer separator to a first irradiation for a first time at a first radiation dose, wherein the first radiation dose ranges from 50-100 kGy; subjecting the polymer separator to a second irradiation for a second time at a second radiation dose, wherein the second radiation dose ranges from 100-200 kGy, and the first time is different from the second time; providing an anode; compressing the polymer separator between the cathode and the anode, wherein the compressed polymer separator is free of crosslinking agent and free of initiator, has a shrinkage of less than 30% at 140°C, and the compressed polymer separator has a thickness between 3 and 30 pm; and providing an electrolyte to form the electrochemical cell; wherein, during the first irradiation and the second irradiation, the polymer separator is maintained at a temperature between 30 and 70°C, and the sum of the first time and the second time is 1-20 hours; and wherein, after the at least one cycle of irradiation of the polymer separator by an energy beam, the polymer separator has a gel content of crosslinked polymer separator of 30% to 90%.

2. The method of claim 1, wherein, The polymer separator is selected from polypropylene, polyethylene, polyvinylidene fluoride, polyimide, polyacrylonitrile, or a combination thereof.

3. The method of claim 1 further comprising: adding a polymer binder on opposite sides of the polymer separator; and adding a plurality of ceramic particles in the polymer binder. The ceramic particles are selected from CaO nanoparticles, MgO nanoparticles, AI2O3 nanoparticles, B2O3 nanoparticles, SiO2 nanoparticles, ZrO2 nanoparticles, SnO2 nanoparticles, nanoclay, or a combination thereof.

4. The method of claim 3, wherein, The polymer binder is selected from silane, acrylate, epoxy, polyurethane, polyolefin, ether, and a combination thereof.

5. The method of claim 3, wherein, 6. The method of claim 1 further comprising: preparing the polymer separator by wet or dry extrusion, electrospinning, melt spinning, or a combination thereof. The energy beam for the at least one cycle of irradiation on the polymer separator is an electron beam.

7. The method of claim 1, wherein, The energy beam for the at least one cycle of irradiation on the polymer separator is a gamma ray.

8. The method of claim 1, wherein, The electrochemical cell comprises:

9. An electrochemical cell prepared by the method of claim 1, wherein, a cathode; an anode; an irradiated polymer separator having a coating, wherein the coating comprises a polymer binder having ceramic particles, wherein the irradiated polymer separator has crosslinked chemical bonds; and an electrolyte; wherein the irradiated polymer separator is free of crosslinking agent and free of initiator, and has a shrinkage of less than 30% at 140°C. The irradiated polymer separator is selected from polypropylene, polyethylene, polyvinylidene fluoride, polyimide, polyacrylonitrile, or a combination thereof.

10. The electrochemical cell of claim 9, wherein the cathode comprises a cathode active material and a cathode binder, and the anode comprises an anode active material and an anode binder. The irradiated polymer separator has a gel content between 30% and 90%.

11. The electrochemical cell of claim 9, wherein the cathode comprises a cathode active material and a cathode binder, and the anode comprises an anode active material and an anode binder. The irradiated polymer separator has a thickness in the range of 3 to 30 pm.

12. The electrochemical cell of claim 9, wherein the cathode comprises a cathode active material and a cathode binder, and the anode comprises an anode active material and an anode binder. The ceramic particles are selected from CaO nanoparticles, MgO nanoparticles, AI2O3 nanoparticles, B2O3 nanoparticles, SiO2 nanoparticles, ZrO2 nanoparticles, SnO2 nanoparticles, nanoclay, or a combination thereof.

13. The electrochemical cell of claim 9, wherein the cathode comprises a cathode active material and a cathode binder, and the anode comprises an anode active material and an anode binder. ​ 14. The electrochemical cell of claim 9, wherein the cathode comprises a cathode active material and a cathode binder, and the anode comprises an anode active material and an anode binder. The polymeric binder is selected from the group consisting of silanes, acrylates, epoxies, polyurethanes, polyolefins, ethers, and combinations thereof.

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