Separator, electrochemical device comprising the same, and method of manufacturing the same
阅读说明：本技术 隔膜，包含该隔膜的电化学装置，和制造该隔膜的方法 (Separator, electrochemical device comprising the same, and method of manufacturing the same ) 是由 程跃 李旭东 闵刚 邓洪贵 陈辉 岳琦 冯超 李祥华 王康 王安 陈阳阳 于 2019-06-24 设计创作，主要内容包括：本发明公开了一种用于电化学装置的隔膜,其包括多孔基膜,位于所述多孔基膜的至少一侧面的涂层和至少一个离子流通道；其中,所述涂层包含至少一种具有例如核-壳结构的有机材料；当所述电化学装置过热至高于所述至少一种有机材料的熔点的温度时,所述有机材料熔化以阻断至少一个离子流通道；以及,本发明还公开了包含该隔膜的电化学装置和制造该隔膜的方法。(A separator for an electrochemical device includes a porous base film, a coating layer and at least one ion flow channel on at least one side of the porous base film; wherein the coating comprises at least one organic material having, for example, a core-shell structure; when the electrochemical device is superheated to a temperature above the melting point of the at least one organic material, the organic material melts to block at least one ion flow channel; also, an electrochemical device comprising the separator and a method of manufacturing the separator are disclosed.)
1. A separator for an electrochemical device, comprising:
a porous base film;
a coating layer on at least one side of the porous base film; and
at least one ion flow channel;
wherein the content of the first and second substances,
the coating comprises at least one organic material having a core-shell structure that melts to block at least one ion flow channel when the electrochemical device is superheated to a temperature above the melting point of the at least one organic material;
wherein the content of the first and second substances,
the core-shell structure includes an inner core and an outer shell, and wherein the outer shell has a melting temperature that is lower than a melting temperature of the inner core.
2. The separator of claim 1, wherein the porous base film comprises at least one selected from the group consisting of polyolefin, aramid, polyamide, and nonwoven fiber.
3. The separator of claim 1, wherein the coating has a thickness ranging from 0.5 to 5 μm.
4. The separator of claim 1, wherein the at least one organic material is selected from the group consisting of polyolefins, modified polyolefins, and oxidized polyolefins.
5. The separator of claim 1, wherein the at least one organic material has a melting point lower than a melting point of the porous base membrane.
6. The separator of claim 1, wherein the at least one organic material is present in the form of particles having an average particle size in the range of 0.01 to 10 μm.
7. The separator of claim 1, wherein the coating further comprises at least one inorganic material.
8. The separator of claim 7, wherein the at least one inorganic material is selected from the group consisting of aluminum oxide (alumina), boehmite (boehmite), silicon dioxide (silica), titanium oxide (titanium oxide), cerium oxide (cerium oxide), calcium oxide (calcium oxide), zinc oxide (zinc oxide), magnesium oxide (magnesium oxide), lithium nitride (lithium nitride), calcium carbonate (calcium carbonate), barium sulfate (barium sulfate), lithium phosphate (lithium phosphate), lithium titanium phosphate (lithium titanate), lithium aluminum phosphate (lithium aluminum phosphate), cerium titanate (cerium titanate), calcium titanate (calcium titanate), barium titanate (barium titanate), and lithium titanate (lanthanum titanate).
9. The separator of claim 7, wherein the at least one inorganic material is present in the form of particles having an average particle size ranging from 0.01 to 10 μm.
10. The separator of claim 7, wherein the coating layer comprises 5 to 40 parts by weight of the at least one organic material and 20 to 60 parts by weight of the inorganic material.
11. The separator of claim 1, further comprising an inorganic layer comprising at least one inorganic material on at least one surface of the coating layer, wherein the coating layer is between the porous base membrane and the inorganic layer.
12. The separator of claim 1, further comprising an inorganic layer comprising at least one inorganic material positioned between the porous base membrane and the coating layer.
13. The separator of claim 1, further comprising an inorganic layer comprising at least one inorganic material, wherein the coating layer and the inorganic layer are respectively located on both sides of the porous base film.
14. The separator of claim 1, wherein the coating further comprises at least one component selected from the group consisting of a binder, a wetting agent, a dispersant, and a thickener.
15. The separator of claim 14, wherein said coating further comprises at least one binder, at least one humectant, at least one dispersant, and at least one thickener.
16. A method of making the separator of claim 1, comprising:
preparing a slurry comprising the at least one organic material and deionized water;
coating the slurry on at least one surface of the porous base film to form a wet coating layer; and the number of the first and second electrodes,
drying the wet coating.
17. The method of claim 16, wherein,
the coating operation is carried out by microgravure coating, knife coating, extrusion coating, spray coating, spin coating or dip coating.
18. A method of making the membrane of claim 7, comprising:
preparing a mixed slurry comprising the at least one organic material, the at least one inorganic material, and deionized water;
coating the mixed slurry on at least one surface of the porous base film to form a wet coating layer; and the number of the first and second electrodes,
drying the wet coating.
19. The method of claim 18, wherein the mixed slurry comprises 5 to 40 parts by weight of the at least one organic material and 20 to 60 parts by weight of the at least one inorganic material, and 40 to 60 parts by weight of the deionized water.
20. The method of claim 18, wherein the mixed slurry further comprises at least one component selected from the group consisting of a binder, a wetting agent, a dispersant, and a thickener.
21. The method of claim 20, wherein the mixed slurry further comprises at least one binder, at least one humectant, at least one dispersant, and at least one thickener.
22. A method of making the membrane of claim 11, comprising:
preparing an organic slurry comprising the at least one organic material and deionized water;
preparing an inorganic slurry comprising the at least one inorganic material, at least one binder, at least one wetting agent, and deionized water;
coating the organic slurry on at least one surface of the porous base film to form a first wet coating layer;
drying the first wet coating to obtain an organic layer;
coating the inorganic slurry on at least one surface of the organic layer to form a second wet coating layer; and the number of the first and second electrodes,
drying the second wet coating.
23. The method of claim 22, wherein the organic paste comprises 20 to 50 parts by weight of the at least one organic material and 50 to 80 parts by weight of deionized water.
24. The method of claim 22, wherein the inorganic slurry comprises 20 to 60 parts by weight of the at least one inorganic material, 2 to 10 parts by weight of the at least one binder, 5 to 20 parts by weight of the wetting agent, and 40 to 60 parts by weight of deionized water.
25. A method of making the membrane of claim 12, comprising:
preparing an organic slurry comprising the at least one organic material and deionized water;
preparing an inorganic slurry comprising the at least one inorganic material, at least one binder, at least one wetting agent, and deionized water;
coating the inorganic slurry on at least one surface of the porous base film to form a first wet coating layer;
drying the first wet coating to obtain an inorganic layer;
coating the organic slurry on at least one surface of the inorganic layer to form a second wet coating layer; and the number of the first and second electrodes,
drying the second wet coating.
26. A method of making the membrane of claim 13, comprising:
preparing an organic slurry comprising the at least one organic material and deionized water;
preparing an inorganic slurry comprising the at least one inorganic material, at least one binder, at least one wetting agent, and deionized water;
coating the organic slurry on one side of the porous base film to form a first wet coating layer;
drying the first wet coating to obtain an organic layer;
coating the inorganic slurry on the other side of the porous base film to form a second wet coating layer, and,
drying the second wet coating.
27. An electrochemical device comprising a positive electrode, a negative electrode and the separator of claim 1 interposed between the positive electrode and the negative electrode.
Technical Field
The present invention relates to a separator for an electrochemical device, an electrochemical device including the same, and a method of manufacturing the same.
Background
As the market for energy storage products grows, batteries and other forms of electrochemical devices are receiving increased attention. For example, lithium secondary batteries have been widely used as energy sources in, for example, mobile phones, notebook computers, electric tools, and electric vehicles.
An electrode assembly of an electrochemical device generally includes a positive electrode, a negative electrode, and a permeable membrane (i.e., a separator) interposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode are prevented from directly contacting each other by the separator, thereby avoiding an internal short circuit. At the same time, ions are allowed to pass through the membrane via channels in the membrane so as to close the circuit during the passage of current. The separator is a key component in an electrochemical device because its structure and properties greatly affect the performance of the electrochemical device, including, for example, internal resistance, energy density, power density, cycle life, and safety; of these properties, safety is always the first requirement.
The separator is typically formed from a polymeric microporous membrane. Commercially available polyolefin-based separators have the advantages of low cost, good chemical stability and excellent mechanical strength. However, they may shrink at high temperatures, producing a volume change and resulting in direct contact of the positive and negative electrodes. In order to reduce heat shrinkage of the polyolefin-based separator, a separator coated with an inorganic material in which a slurry containing inorganic particles and a binder polymer is coated on at least one surface of the polyolefin-based separator is pushed out. In the inorganic material-coated separator, the inorganic particles in the coating layer can serve as a support for maintaining the mechanical shape of the separator and can help prevent the polyolefin-based film from heat shrinkage when the electrochemical device is overheated. In addition, when the temperature of the electrochemical device is higher than the melting point of the polyolefin in the base film, the polyolefin in the porous base film may melt to close the pores of the base film, and thus, ions may be prevented from passing through the separator, which may cause the shutdown of the electrochemical device.
In order to ensure the safety of the electrochemical device in a high temperature environment, it is still required to develop a separator having a low thermal shrinkage rate and an effective shutdown mechanism.
Disclosure of Invention
The present invention provides a separator for an electrochemical device. Specifically, the separator disclosed herein includes a porous base membrane, a coating layer disposed on at least one side of the porous base membrane, and at least one ion flow channel. The coating includes at least one organic material that melts to block at least one ion flow path when the electrochemical device is overheated to a temperature above the melting point of the at least one organic material. In some embodiments of the present invention, the at least one organic material has a core-shell structure comprising an inner core and an outer shell, wherein the outer shell has a melting temperature different from the melting temperature of the inner core; for example, the melting temperature of the outer shell is lower than the melting temperature of the inner core. At least one ion flow channel of the membranes disclosed herein can be blocked at different temperatures. Batteries containing the separators disclosed herein can be shut down at a temperature between the melting temperature of the outer shell and the melting temperature of the inner core. In some embodiments of the invention, the coating comprises at least two organic materials having a core-shell structure comprising an inner core of one organic material and an outer shell of another organic material, wherein the melting temperature of the outer shell is different from the melting temperature of the inner core, e.g., the melting temperature of the outer shell is lower than the melting temperature of the inner core.
The present invention also provides methods of making the membranes disclosed herein.
In one embodiment of the present invention, a method of making a separator disclosed herein comprises: preparing a slurry comprising at least one organic material and deionized water; applying the slurry to at least one surface of a porous base membrane to form a wet coating; and drying the wet coating.
In another embodiment of the present invention, a method of making a separator disclosed herein comprises: preparing a mixed slurry comprising at least one organic material, at least one inorganic material, and deionized water; applying the mixed slurry to at least one surface of a porous base film to form a wet coating layer; and drying the wet coating.
In another embodiment of the present invention, a method of making a separator disclosed herein comprises: preparing an organic slurry comprising at least one organic material and deionized water; preparing an inorganic slurry comprising at least one inorganic material, at least one binder, at least one wetting agent, and deionized water; applying the organic slurry to at least one surface of a porous base film to form a first wet coating layer; drying the first wet coating to obtain an organic layer; applying the inorganic slurry to at least one surface of the organic layer to form a second wet coating; and drying the second wet coating.
In a preferred embodiment of the present invention, a method of manufacturing a separator disclosed herein comprises: preparing an organic slurry comprising at least one organic material and deionized water; preparing an inorganic slurry comprising at least one inorganic material, at least one binder, at least one wetting agent, and deionized water; coating the inorganic slurry onto at least one surface of a porous base film to form a first wet coating layer; drying the first wet coating to obtain an inorganic layer; applying the organic slurry to at least one surface of the inorganic layer to form a second wet coating; and drying the second wet coating.
In another embodiment of the present invention, a method of making a separator disclosed herein comprises: preparing an organic slurry comprising at least one organic material and deionized water; preparing an inorganic slurry comprising at least one inorganic material, at least one binder, at least one wetting agent, and deionized water; applying the organic slurry to one surface of a porous base film to form a first wet coating layer; drying the first wet coating to obtain an organic layer; coating the inorganic slurry onto the other surface of the porous base film to form a second wet coating layer; and drying the second wet coating.
The invention also discloses an electrochemical device. The electrochemical devices disclosed herein comprise a positive electrode, a negative electrode, and the separator disclosed herein interposed between the positive electrode and the negative electrode.
Drawings
FIG. 1 illustrates a schematic view of an exemplary septum 100 according to a specific embodiment disclosed herein;
FIG. 2 illustrates a schematic view of an exemplary septum 200 according to another specific embodiment disclosed herein;
FIG. 3 illustrates a schematic view of an exemplary septum 300 according to yet another specific embodiment disclosed herein;
FIG. 4 illustrates a schematic view of an exemplary septum 400 according to yet another specific embodiment disclosed herein;
FIG. 5 illustrates a schematic view of an exemplary septum 500 according to yet another specific embodiment disclosed herein;
fig. 6 is a Scanning Electron Microscope (SEM) image of the separator prepared in example 6 before heat treatment in test 1;
fig. 7 is a Scanning Electron Microscope (SEM) image of the separator prepared in example 6 after heat treatment in test 1.
Detailed description of the preferred embodiments
The present application provides some exemplary embodiments of a separator for an electrochemical device. In some embodiments of the present application, the coating comprises at least one layer of organic material on at least one side of the porous base membrane. The coating may be on only one side of the porous base membrane. For example, as shown in fig. 1, the separator 100 includes a porous base film 101 and a coating layer 103, the coating layer 103 including at least one organic material formed on one surface of the porous base film 101. In some other embodiments, the coating may be on both sides of the porous base membrane.
A porous base film is used as the substrate. The porous base membrane disclosed herein may have a thickness ranging, for example, from 0.5 to 50 μm, such as from 0.5 to 20 μm, and further such as from 5 to 18 μm. The porous base film may have a number of pores inside through which gas, liquid or ions can be transferred from one side surface to the other side surface of the porous base film.
Any suitable porous membrane having an average pore diameter in the range of, for example, 0.01 to 50 μm, such as 0.1 to 20 μm, further, such as 0.5 to 10 μm, may be used as the porous base membrane. Various materials, organic or inorganic, may be used to prepare the porous base membrane. For example, the porous base film may include at least one selected from the group consisting of polyolefin, aramid, polyamide, and various nonwoven fibers.
In some embodiments herein, a polyolefin-based porous film may be used as the porous base film. Examples of the polyolefin contained in the polyolefin-based porous film may include Polyethylene (PE), High Density Polyethylene (HDPE), polypropylene (PP), polybutene, polypentene, polymethylpentene (TPX), copolymers thereof, and mixtures thereof. The weight average molecular weight (Mw) of the polyolefins disclosed herein may range, for example, from 50,000 to 2,000,000, such as from 100,000 to 1,000,000. The average pore diameter of the pores in the polyolefin-based porous base film may range, for example, from 20 to 70nm, such as from 30 to 60 nm. The porosity of the polyolefin-based porous base film may range, for example, from 25% to 50%, such as from 30% to 45%. In addition, the polyolefin-based porous base film may have a gas permeability range of, for example, 50 to 400 seconds/100 ml, such as 80 to 300 seconds/100 ml. In addition, the polyolefin-based porous base film may have a single layer structure or a multi-layer structure. The polyolefin-based porous base film having a multi-layer structure may include at least two laminated polyolefin-based layers including, for example, different types of polyolefins or the same type of polyolefins having different molecular weights. The polyolefin-based porous base film disclosed herein may be prepared according to a conventional method known in the art, or may be directly purchased in the market.
In some other embodiments, the nonwoven membrane may form at least a portion of the porous base membrane. The term "nonwoven membrane" refers to a composite membrane comprising a plurality of randomly distributed fibers forming a network between the fibers. These fibers may or may not generally be bonded to each other. These fibers may be staple fibers (i.e., discontinuous fibers having a length of no more than 10 cm) or continuous fibers. These fibers may comprise a single material or a plurality of materials, either a combination of different fibers, or a combination of similar fibers each comprising a different material. The nonwoven films disclosed herein, for example, exhibit dimensional stability, i.e., a heat shrinkage of less than 5% when heated to 100 ℃ in about two hours. The nonwoven membrane may have a relatively large average pore size, for example, in the range of 0.1 to 20 μm, such as 1 to 5 μm. The porosity of the nonwoven film may be, for example, from 40% to 80%, such as from 50% to 70%. Further, the nonwoven film may have an air permeability, for example, of less than 500 seconds/100 ml, such as in the range of from 0 to 400 seconds/100 ml, and further such as in the range of from 0 to 200 seconds/100 ml. Some examples of the nonwoven film are formed from at least one material selected from the group consisting of: polyethylene (PE), High Density Polyethylene (HDPE), polypropylene (PP), polybutylene, polypentene, polymethylpentene (TPX), polyethylene terephthalate (PET), polyamide, Polyimide (PI), Polyacrylonitrile (PAN), viscose, polyester, polyacetal, polycarbonate, Polyetherketone (PEK), Polyetheretherketone (PEEK), polybutylene terephthalate (PBT), Polyethersulfone (PEs), polyphenylene oxide (PPO), Polyphenylene Sulfide (PPs), polyethylene naphthalene (PEN), cellulose fibers, and copolymers thereof. In one embodiment, a nonwoven film formed of PET is used as the porous base film. The nonwoven porous membranes disclosed herein may be prepared according to conventional methods known in the art, such as electrospraying, electrospinning, and meltblowing, or may be purchased directly on the market.
In addition to porous base films, the coatings disclosed herein can also have a porous structure that allows passage of gases, liquids, or ions from one surface of the coating to the other. Since both the porous base membrane and the coating layer are porous, the separator disclosed herein has at least one ion flow channel passing from one side surface to the other side surface.
The coating layer of the separator disclosed herein may include at least one organic material that melts to block at least one ion flow channel in the separator when the electrochemical device is overheated to a temperature higher than a melting point of the at least one organic material. Therefore, when the ion current is blocked, the electrochemical device may be turned off, thereby ensuring the safety of the electrochemical device. When the electrochemical device is overheated, if at least one ion flow channel in the separator is not closed, the temperature of the electrochemical device may continue to increase, resulting in deformation or rupture of the separator and internal short circuits. The internal short circuit may cause some accidents such as swelling of the battery, burning or explosion, etc.
In some embodiments, the melting point of the at least one organic material may range, for example, from 60 ℃ to 150 ℃, such as from 90 ℃ to 120 ℃. In addition, the melting point of the at least one organic material may depend on the requirements of the electrochemical device, e.g., various usages and operating environments. Once the desired melting point is determined, the particular organic material having the desired melting point will be selected for use in preparing the coating of the separator. For example, when it is desired to shut down the battery at 110 ℃, an organic material (e.g., PE particles) having a melting point of about 110 ℃ may be used to prepare a coating for a separator in the battery. Furthermore, for example, when it is desired to shut down the battery at a temperature between 80 ℃ and 120 ℃, an organic material having a melting point temperature of the outer shell of 80 ℃ and a melting point temperature of the inner core of 120 ℃ may be used to prepare a coating layer for a separator used in the battery.
In some embodiments, the at least one organic material may have a melting point lower than the melting point of the porous base film. The porous base membrane may maintain its original size or hardly shrink when at least one organic material in the coating layer is melted to block at least one ion flow channel, thereby preventing a short circuit of the positive electrode and the negative electrode.
A variety of organic materials having suitable melting points may be used as at least one organic material in the present application. For example, the at least one organic material may be a polyolefin or polyolefin derivative, such as a modified polyolefin and an oxidized polyolefin. The polyolefins disclosed herein may include polyolefins having a density of 0.94 to 0.98g/cm3And a high density polyolefin having a density of 0.91 to 0.94g/cm3A low density polyolefin of (a). The modified polyolefins disclosed herein may be obtained by at least one of a variety of modification methods, including, for example, grafting, copolymerization, crosslinking, and blending. The oxidized polyolefins disclosed herein may be obtained, for example, by ring-opening polymerization of alkylene oxides (alkylene oxides) under heterogeneous catalysis.
In some embodiments, the at least one organic material may be present in the coating in the form of particles having, for example, a core-shell structure. The average particle size of the particles of the at least one organic material ranges, for example, from 0.01 to 10 μm, such as from 0.05 to 5 μm, and further such as from 0.3 to 2 μm.
The at least one organic material may be uniformly or non-uniformly distributed in the coating layer, as long as a majority (e.g., 80% to 95%) of the ion flow channels in the membrane can be blocked when the at least one organic material melts. In one embodiment, the particles of the at least one organic material are distributed in the coating layer such that the surface of the porous base membrane is not visible to the naked eye from the top.
In some embodiments, the coating may further comprise at least one inorganic material. For example, as shown in fig. 2, the separator 200 includes a porous base film 201 and a coating layer 203 including at least one organic material and at least one inorganic material formed on one surface of the porous base film 201. The presence of the at least one inorganic material may improve heat resistance of the separator and reduce heat shrinkage of the porous base film at high temperatures. A variety of inorganic particles may be used as the at least one inorganic material, including, for example, oxides, hydroxides, sulfides, nitrides, carbides, carbonates, sulfates, phosphates, and titanates, as well as elements such as at least one of metals and semiconductors, such as Si, Al, Ca, Ti, B, Sn, Mg, Li, Co, Ni, Sr, Ce, Zr, Y, Pb, Zn, Ba, and La. For example, alumina (Al)2O3) Boehmite (gamma-AlOOH), Silica (SiO)2) Titanium dioxide (TiO)2) Cerium oxide (CeO)2) Calcium oxide (CaO), zinc oxide (ZnO), magnesium oxide (MgO), and lithium nitride (Li)3N), calcium carbonate (CaCO)3) Barium sulfate (BaSO)4) Lithium phosphate (Li)3PO4) Lithium Titanium Phosphate (LTPO), Lithium Aluminum Titanium Phosphate (LATP), cerium titanate (CeTiO)3) Calcium titanate (CaTiO)3) Barium titanate (BaTiO)3) And Lanthanum Lithium Titanate (LLTO) may be used as the inorganic material. The average particle size of the inorganic materials disclosed herein can range, for example, from 0.01 to 10 μm, such as from 0.5 to 5 μm. In some embodiments, the at least one organic material and the at least one inorganic material may have similaritiesThe average particle diameter of (3). For example, both organic and inorganic materials have particle sizes on the order of nanometers or microns.
When the at least one organic material and the at least one inorganic material are simultaneously present in the coating layer, the weight ratio of the two components may be controlled within a range to ensure that thermal shrinkage of the porous base film may be minimized and/or prevented and effective shutdown may be achieved when the electrochemical device is overheated. In some embodiments, the coating may comprise 5 to 40 parts by weight of the at least one organic material and 20 to 60 parts by weight of the at least one inorganic material. For example, the coating may comprise 20 to 30 parts by weight of the at least one organic material and 30 to 50 parts by weight of the at least one inorganic material.
In some embodiments, the coating may further comprise at least one agent selected from the group consisting of binders, wetting agents, dispersants, and thickeners. For example, the coating may further comprise at least one binder, at least one humectant, at least one dispersant, and at least one thickener.
The at least one binder disclosed herein may be selected from, for example, acrylate, methacrylate, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethyl acrylate, polyethylacrylate, pure acrylate, copolymer of polyacrylic acid and polystyrene, polyvinylpyrrolidone, styrene-butadiene rubber, nitrile rubber (nitrile rubber), epoxy resin (epoxy resin), neopentyl glycol diacrylate (neopentylglycol diacrylate), sodium polyacrylate (sodium polyacrylate), polytetrafluoroethylene (polytetrafluoroethylene), polyimide (polyimide), polyamide (polyamide), polyester (polyester), cellulose derivative (cellulose derivative), polysulfone (polysulfone), and copolymers thereof. The at least one wetting agent disclosed herein may be selected from, for example, polyoxyethylene alkanolamides (alkylolamides), sulfonated oils (sulfonated oils), fatty acid salts (fatty acid salt), sodium dibutyl naphthalene sulfonate (sodium dibutyl naphthalene sulfonate), soybean lecithin (soybean bean lecithin), thiols (thiol), hydrazides (hydrazides), copolymers of polyethers and silicones (copolymer of polyethers and organosiloxanes), and mercaptals (mercaptals). The at least one thickener disclosed herein may be selected from, for example, methyl cellulose (methyl cellulose), carboxymethyl cellulose (carboxymethyl cellulose), hydroxyethyl cellulose (hydroxyethyl cellulose), hydroxypropyl methyl cellulose (hydroxypropyl methyl cellulose), and salts thereof. The at least one dispersant disclosed herein may be selected from, for example, a copolymer of polyether and silicone (copolymer of polyether and organosilicon), polyethylene oxide (PEO), polyvinyl alcohol (polyvinyl alcohol), sodium polyacrylate (sodium polyacrylate), silicate (silicate), phosphate (phosphate), sodium dodecyl sulfate (sodium dodecyl sulfate), methyl amyl alcohol (methyl pentanol), cellulose derivative (cellulose derivative), polyacrylamide (polyacrylamide), guar gum (gum), and polyethylene glycol fatty acid ester (fatty acid ester).
In some embodiments, the coating may be applied to the porous base film as a slurry using a suitable technique such as micro-gravure coating, blade coating, extrusion coating, spray coating, spin coating, or dip coating. At least a portion of the slurry may penetrate into the pores of the porous base membrane.
In addition, the thickness of the coating layer of the separator disclosed herein may range, for example, from 0.1 to 10 μm, such as from 0.5 to 5 μm.
In some embodiments, the separator disclosed herein may further comprise an inorganic layer comprising the at least one inorganic material. Three embodiments are shown in fig. 3, 4 and 5, respectively.
Fig. 3 shows a separator 300 comprising a porous base membrane 301, a coating layer 303 containing the at least one organic material, and an inorganic layer 305 containing the at least one inorganic material. The coating layer 303 is disposed on one surface of the porous base film 301, and the inorganic layer 305 is disposed on at least one surface of the coating layer 303, and thus, the coating layer 303 is located between the porous base film 301 and the inorganic film. In some embodiments, the other side of the porous base membrane 301 may be coated with an additional layer containing at least one organic or inorganic material, for example, an adhesive polymer such as polyvinylidene fluoride (PVDF).
Fig. 4 shows a separator 400 comprising a porous base membrane 401, a coating layer 403 comprising the at least one organic material, and an inorganic layer 405 comprising the at least one inorganic material. The inorganic layer 405 is disposed between the porous base film 401 and the coating layer 403. In some embodiments, the other side of the porous base membrane 401 may be coated with an additional layer containing at least one organic or inorganic material, for example, an adhesive polymer such as polyvinylidene fluoride (PVDF).
Fig. 5 shows a separator 500 comprising a porous base membrane 501, a coating layer 503 comprising the at least one organic material, and an inorganic layer 505 comprising the at least one inorganic material. The coating layer 503 and the inorganic layer 505 are respectively provided on both sides of the porous base film 501. In some embodiments, an additional layer comprising at least one organic or inorganic material, for example, an adhesive polymer (binding polymer) such as polyvinylidene fluoride (PVDF), may be formed on the outer side of the coating 503 or the inorganic layer 505.
The at least one inorganic material present in the inorganic layer disclosed herein may be selected from, for example, aluminum oxide (Al)2O3) Boehmite (gamma-AlOOH), Silica (SiO)2) Titanium dioxide (TiO)2) Cerium oxide (CeO)2) Calcium oxide (CaO), zinc oxide (ZnO), magnesium oxide (MgO), and lithium nitride (Li)3N), calcium carbonate (CaCO)3) Barium sulfate (BaSO)4) Lithium phosphate (Li)3PO4) Lithium Titanium Phosphate (LTPO), Lithium Aluminum Titanium Phosphate (LATP), cerium titanate (CeTiO)3) Calcium titanate (CaTiO)3) Barium titanate (BaTiO)3) And Lanthanum Lithium Titanate (LLTO). Additionally, the at least one inorganic material may have an average particle size in a rangeAnd is, for example, 0.01 to 10 μm, such as 0.5 to 5 μm.
Further disclosed herein are embodiments of methods of making the separator of the present application. In some embodiments, the method comprises a wet coating process.
One embodiment of a method of manufacturing the diaphragm 100 shown in FIG. 1 includes:
preparing a slurry comprising the at least one organic material and deionized water;
coating the slurry on at least one surface of a porous base film to form a wet coating layer; and the number of the first and second electrodes,
the wet coating is dried.
The slurry prepared in the above method may include 20 to 50 parts by weight of the at least one organic material and 50 to 80 parts by weight of deionized water. In some embodiments, the slurry may further comprise 5 to 10 parts by weight of at least one agent selected from the group consisting of binders, wetting agents, dispersants, and thickeners. The coating operation can be carried out by microgravure coating, knife coating, extrusion coating, spray coating, spin coating or dip coating. The wet coating may be dried by heating, for example in an oven at a temperature in the range, for example, from 50 ℃ to 90 ℃, such as from 60 ℃ to 80 ℃.
One embodiment of a method of manufacturing the diaphragm 200 shown in FIG. 2 includes:
preparing a mixed slurry comprising the at least one organic material, the at least one inorganic material, and deionized water;
coating the mixed slurry on at least one surface of the porous base film to form a wet coating layer; and the number of the first and second electrodes,
drying the wet coating.
The slurry prepared in the above method may include 5 to 40 parts by weight of the at least one organic material and 20 to 60 parts by weight of the at least one inorganic material, and 40 to 60 parts by weight of deionized water. In some embodiments, the slurry may further comprise 2 to 10 parts by weight of at least one binder. In some embodiments, the slurry may further comprise 5 to 20 parts by weight of at least one agent selected from the group consisting of wetting agents, dispersing agents, and thickening agents.
In some embodiments, the mixed slurry may be stirred to form a homogeneous slurry. Thus, the coating 203 may have a substantially uniform structure, i.e., the at least one organic material and/or the at least one inorganic material may be substantially uniformly or uniformly distributed in the coating.
One embodiment of a method of manufacturing the diaphragm 300 shown in FIG. 3 includes:
preparing an organic slurry comprising the at least one organic material and deionized water;
preparing an inorganic slurry comprising the at least one inorganic material, at least one binder, at least one wetting agent, and deionized water;
coating an organic slurry on at least one surface of a porous base film to form a first wet coating layer;
drying the first wet coating to obtain an organic layer;
coating an inorganic slurry on at least one surface of the organic layer to form a second wet coating layer; and the number of the first and second electrodes,
the second wet coating is dried.
In some embodiments, the organic slurry prepared in the above method may include 20 to 50 parts by weight of the at least one organic material and 50 to 80 parts by weight of deionized water. In some embodiments, the inorganic slurry prepared in the above method may include 20 to 60 parts by weight of at least one inorganic material, 2 to 10 parts by weight of at least one binder, 5 to 20 parts by weight of a wetting agent, and 40 to 60 parts by weight of deionized water.
One embodiment of a method of manufacturing the diaphragm 400 shown in FIG. 4 includes:
preparing an organic slurry comprising the at least one organic material and deionized water;
preparing an inorganic slurry comprising the at least one inorganic material, at least one binder, at least one wetting agent, and deionized water;
coating an inorganic slurry on at least one surface of a porous base film to form a first wet coating layer;
drying the first wet coating to obtain an inorganic layer;
coating an organic slurry on at least one surface of the inorganic layer to form a second wet coating layer; and the number of the first and second electrodes,
the second wet coating is dried.
In some embodiments, the organic slurry prepared in the above method may include 20 to 50 parts by weight of the at least one organic material and 50 to 80 parts by weight of deionized water. In some embodiments, the inorganic slurry prepared in the above method may include 20 to 60 parts by weight of the at least one inorganic material, 2 to 10 parts by weight of the at least one binder, 5 to 20 parts by weight of the wetting agent, and 40 to 60 parts by weight of deionized water.
One embodiment of a method of manufacturing the septum 500 shown in figure 5 includes:
preparing an organic slurry comprising the at least one organic material and deionized water;
preparing an inorganic slurry comprising the at least one inorganic material, at least one binder, at least one wetting agent, and deionized water;
coating an organic slurry on one side of a porous base film to form a first wet coating layer;
drying the first wet coating to obtain an organic layer;
coating an inorganic slurry on the other side of the porous base film to form a second wet coating layer; and is
The second wet coating is dried.
In some embodiments, the organic slurry prepared in the above method may include 20 to 50 parts by weight of the at least one organic material and 50 to 80 parts by weight of deionized water. In some embodiments, the inorganic slurry prepared in the above method may include 20 to 60 parts by weight of the at least one inorganic material, 2 to 10 parts by weight of the at least one binder, 5 to 20 parts by weight of the wetting agent, and 40 to 60 parts by weight of deionized water.
The thickness of the separator disclosed herein can be controlled according to the requirements of an electrochemical device (e.g., a lithium ion battery).
In one embodiment, the separator disclosed herein comprises a porous base membrane and a coating layer comprising at least one organic material. When the electrochemical device is overheated above the melting point of the at least one organic material, the at least one organic material melts to block the at least one ion flow channel, thereby shutting down the electrochemical device for safety. The separator disclosed herein can also have a low thermal shrinkage rate at high temperatures to avoid short circuits. The separator disclosed herein has a wide range of applications and can be used to manufacture high energy density and/or high power density batteries in many stationary and portable devices, for example, batteries for automobiles, batteries for medical devices, and batteries for other large devices.
Further, the present application provides an electrochemical device comprising: a positive electrode, a negative electrode, and a separator as disclosed herein, the separator being interposed between the positive electrode and the negative electrode. The electrochemical device of the present application may further include an electrolyte. The separator is sandwiched between the positive electrode and the negative electrode to prevent the occurrence of physical contact and short circuit between the two electrodes. The porous structure of the separator ensures that ionic charge carriers (e.g., lithium ions) pass between the positive and negative electrodes. Additionally, the separator disclosed herein may also provide mechanical support for the electrochemical device. The electrochemical devices disclosed herein include any device in which electrochemical reactions occur. For example, the electrochemical device disclosed herein includes primary batteries (primary batteries), secondary batteries (secondary batteries), fuel cells, solar cells, and capacitors. In some embodiments, the electrochemical device disclosed herein is a lithium secondary battery (a lithium secondary battery), such as a lithium metal secondary battery (a lithium metal secondary battery), a lithium ion secondary battery (a lithium ion secondary battery), a lithium polymer secondary battery (a lithium polymer secondary battery), and a lithium sulfur secondary battery (a lithium sulfur secondary battery).
With the separator of the present application inside, as described above, the electrochemical device disclosed herein can exhibit higher safety at high temperatures.
The electrochemical devices disclosed herein may be manufactured by conventional methods known to those skilled in the art. In one embodiment, an electrode assembly is formed by placing the separator of the present application between a positive electrode and a negative electrode, and an electrolyte is injected into the electrode assembly. The electrode assembly may be formed through a conventional process such as a winding process or a stacking and folding process.
Reference is made in particular to the following examples. It should be understood that the following examples are illustrative only, and the present application is not limited thereto.
Example 1
An inorganic slurry is prepared. 1 part by weight of an aqueous solution (41-43 wt%) of sodium polyacrylate and 40 parts by weight of alumina (average particle diameter of 0.5 μm) were added to 48 parts by weight of deionized water to obtain a mixture. After the mixture was stirred and ground in a grinder for 25 minutes, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose and 1 part by weight of a copolymer (Mw of 6,000) of polyether and silicone were added to the mixture, and dispersed with stirring. To the mixture, 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate was added and dispersed by stirring to obtain the inorganic slurry.
An organic slurry is prepared. 40 parts by weight of an organic core-shell PE powder (average particle diameter of 0.5 μm, Mw of 50,000, density of 0.93 g/cm)3The melting point of the outer shell was 80 ℃ and the melting point of the inner core was 110 ℃) to 55 parts by weight of deionized water, and dispersed by stirring to obtain a mixture. To the mixture, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose was added and dispersed by stirring to obtain the organic slurry.
And (4) preparing the diaphragm. The inorganic slurry was coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet inorganic layer (a wet inorganic layer), which was then dried at 80 ℃. The organic slurry was coated on the outer side of the inorganic layer to obtain a wet organic layer (a wet organic layer), which was then dried at 80 ℃.
Example 2
The inorganic slurry was prepared by following the same procedure as that for preparing the inorganic slurry in example 1 described above.
An emulsion of 20 wt% core-shell PE particles was used directly as the organic slurry. The organic core-shell PE particles dispersed in the core-shell PE emulsion had an average particle diameter of 0.5 μm, M w of 50,000, a density of 0.93g/cm3, a melting point of the outer shell of 80 ℃, and a melting point of the inner core of 110 ℃.
And (4) preparing the diaphragm. The organic slurry was coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet organic layer (a wet organic layer), which was then dried at 80 ℃. The inorganic slurry was coated on the outer side of the organic layer to obtain a wet inorganic layer (a wet inorganic layer), which was then dried at 80 ℃.
Example 3
The inorganic slurry was prepared by following the same procedure as that for preparing the inorganic slurry in example 1 described above.
The emulsion of core-shell PE particles in example 2 above was used as the organic slurry.
And (4) preparing the diaphragm. The inorganic slurry was coated on both sides of a porous PE film having a thickness of 12 μm to obtain a wet inorganic layer on each side, which was then dried at 80 ℃. The organic slurry was coated on the outer side of each inorganic layer to obtain a wet organic layer on each side, which was then dried at 80 ℃. A separator having a five-layer structure was obtained.
Example 4
The inorganic slurry was prepared by following the same procedure as that for preparing the inorganic slurry in example 1 described above.
The emulsion of core-shell PE particles in example 2 above was used as the organic slurry.
And (4) preparing the diaphragm. On one side of a porous PE film having a thickness of 12 μm, an organic slurry was coated first, and then dried at 80 ℃ to obtain an organic layer; the inorganic slurry was coated on the outer surface of the organic layer, and then dried at 80 ℃. On the other side of the porous PE film, an inorganic slurry was coated, followed by drying at 80 ℃ to obtain an inorganic layer, and then an inorganic slurry was coated on the outer surface of the inorganic layer and then dried at 80 ℃. A separator having a five-layer structure was obtained.
Example 5
A mixed slurry is prepared. 1 part by weight of an aqueous solution (41-43 wt%) of sodium polyacrylate and 5 parts by weight of alumina (average particle diameter of 1 μm) were added to 33 parts by weight of deionized water to obtain a mixture. After the mixture was stirred and ground in a grinder for 25 minutes, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose and 1 part by weight of a copolymer (Mw of 6,000) of polyether and silicone were added to the mixture and dispersed by stirring. To this mixture, 50 parts by weight of an emulsion of core-shell PE particles (40 wt%, the average particle diameter of the core-shell PE particles dispersed in the emulsion of core-shell PE particles was 2 μm, Mw was 150,000, density was 0.96g/cm3, melting point of the outer shell was 110 ℃, and melting point of the inner core was 140 ℃). Finally, 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate was added to the mixture and dispersed by stirring to obtain the mixed slurry.
And (4) preparing the diaphragm. The mixed slurry was uniformly coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet coating, which was then dried at 80 ℃.
Example 6
A mixed slurry is prepared. 1 part by weight of an aqueous solution (41-43 wt%) of sodium polyacrylate and 10 parts by weight of alumina (average particle diameter of 1 μm) were added to 53 parts by weight of deionized water to obtain a mixture. After the mixture was stirred and ground in a grinder for 25 minutes, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose and 1 part by weight of a copolymer (Mw of 6,000) of polyether and silicone were added to the mixture and dispersed by stirring. 25 parts by weight of an emulsion of core-shell PE particles (40% by weight, the average particle diameter of the core-shell PE particles dispersed in the emulsion of core-shell PE particles was 2 μm, Mw was 150,000, and the density was 0.96g/cm3The melting point of the shell is 110 ℃ and the melting point of the core is 140 ℃. ) Is added to the mixture. Finally, 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate was added to the mixture and dispersed by stirring to obtain a mixed slurry.
And (4) preparing the diaphragm. The mixed slurry was uniformly coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet coating, which was then dried at 80 ℃.
Example 7
A mixed slurry is prepared. 1 part by weight of an aqueous solution (41-43 wt%) of sodium polyacrylate and 20 parts by weight of alumina (average particle diameter of 1 μm) were added to 55 parts by weight of deionized water to obtain a mixture. After the mixture was stirred and ground in a grinder for 25 minutes, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose and 1 part by weight of a copolymer (Mw of 6,000) of polyether and silicone were added to the mixture and dispersed by stirring. 13 parts by weight of an emulsion of core-shell PE particles (40% by weight, the average particle diameter of the core-shell PE particles dispersed in the emulsion of core-shell PE particles was 2 μm, Mw was 150,000, and the density was 0.96g/cm3The melting point of the shell is 110 ℃ and the melting point of the core is 140 ℃. ) Is added to the mixture. Finally, 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate was added to the mixture and dispersed by stirring to obtain a mixed slurry.
And (4) preparing the diaphragm. The mixed slurry was uniformly coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet coating layer, which was then dried at 80 ℃.
Example 8
The same procedure for producing a separator as in example 7 above was used to produce a separator, except that both sides of the PE-based film were coated with the mixed slurry.
Example 9
The same procedure for preparing a separator as in example 7 above was used except that silica (average particle diameter of 1 μm) was used instead of alumina to prepare a separator.
Example 10
Except that an emulsion of core-shell polybutene (a core-shell polybutene emulsion) (40 wt%) was used, and the core-shell polybutene particles dispersed in the emulsion of core-shell polybutene had an average particle diameter of 0.5 μm, Mw of 200,000, 0.91g/cm3The melting point of the shell is 110 ℃ and the melting point of the core is 140 ℃. ) The same procedure for preparing a separator as in example 7 above was used instead of the PE emulsion.
Example 11
And (4) preparing the diaphragm. An emulsion of core-shell PE particles (40 wt%, core-shell PE particles dispersed in the emulsion of core-shell PE particles had an average particle diameter of 2 μm, Mw of 80,000, 0.92g/cm3Has a melting point of 110 ℃ for the outer shell and 140 ℃ for the inner core) was uniformly coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet coating layer, which was then dried at 80 ℃.
Example 12
And (4) preparing the diaphragm. Emulsion of core-Shell PE particles (40 wt%, core-Shell PE particles dispersed in the emulsion of core-Shell PE particles have an average particle size of 2 μm, Mw of 80,000, 0.92g/cm3The melting point of the outer shell was 110 c and the melting point of the inner core was 140 c) were uniformly coated on both sides of a porous PE film having a thickness of 12 μm to obtain a wet coating layer, which was then dried at 80 c.
Comparative example 1
An inorganic slurry is prepared. 1 part by weight of an aqueous solution (41-43 wt%) of sodium polyacrylate and 40 parts by weight of alumina (average particle diameter of 2 μm) were added to 48 parts by weight of deionized water to obtain a mixture. After the mixture was stirred and ground in a grinder for 25 minutes, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose and 1 part by weight of a copolymer (Mw of 6,000) of polyether and silicone were added to the mixture and dispersed by stirring. To the mixture was added 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate, and dispersed by stirring to obtain an inorganic slurry.
And (4) preparing the diaphragm. The inorganic slurry was uniformly coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet inorganic layer, which was then dried at 80 ℃.
Comparative example 2
The same procedure for preparing a separator as in comparative example 1 above was used except that silica (average particle diameter of 1 μm) was used instead of alumina.
Comparative example 3
And preparing slurry. 1 part by weight of an aqueous solution (41-43 wt%) of sodium polyacrylate and 25 parts by weight of alumina (average particle diameter of 1 μm) were added to 58 parts by weight of deionized water to obtain a mixture. After the mixture was stirred and ground in a grinder for 25 minutes, 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose and 1 part by weight of a copolymer (Mw of 6,000) of polyether and silicone were added to the mixture and dispersed by stirring. 5 parts by weight of PVDF powder (average particle diameter 0.5 μm) were added to the mixture. Finally, 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate was added to the mixture and dispersed by stirring to obtain a PVDF/alumina slurry.
And (4) preparing the diaphragm. A PVDF/alumina slurry was uniformly coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet layer, which was then dried at 80 ℃.
Comparative example 4
The inorganic slurry was prepared by following the same procedure as that for preparing the inorganic slurry in example 1 described above.
And preparing PVDF slurry. 40 parts by weight of PVDF powder (average particle size of 0.5 μm) was added to 50 parts by weight of deionized water, and dispersed by stirring to obtain a mixture. To the mixture was added 5 parts by weight of an aqueous solution (4 wt%) of sodium carboxymethylcellulose, and dispersed by stirring. Finally, 5 parts by weight of an aqueous solution (45 wt%) of methyl acrylate was added to the mixture, and dispersed by stirring to obtain PVDF slurry.
And (4) preparing the diaphragm. The inorganic slurry was coated on one side of a porous PE film having a thickness of 12 μm to obtain a wet inorganic layer, which was then dried at 80 ℃. The PVDF slurry was coated on the outer side of the inorganic layer to obtain a wet PVDF layer, which was then dried at 80 ℃.
Comparative example 5
A porous PE film having a thickness of 12 μm was directly used as the separator.
The following tests 1 to 4 were performed on the separators prepared in examples 1 to 12 and comparative examples 1 to 5. The test results are shown in Table 1.
Test 1: high temperature stability
The separators prepared in examples 1 to 10 and comparative examples 1 to 4 were maintained at 120 ℃ for 1 hour to be heat-treated. The separators prepared in examples 11 to 12 were kept at 105 ℃ for 1 hour to be heat-treated. Two samples of the separator of comparative example 5 were heat-treated at 120 ℃ and 105 ℃ for 1 hour, respectively.
The separator after the above heat treatment was inspected and observed with the naked eye. If the separator is deformed, or the surface of the separator is wrinkled, uneven, curled or spotted, it is unstable at the test temperature. Otherwise, the separator is stable at the test temperature.
And (3) testing 2: thermal shrinkage
For each of the separators prepared in examples 1 to 12 and comparative examples 1 to 5, the thermal shrinkage in the Transverse Direction (TD) after the heat treatment in test 1 was measured using a binary optics projector.
And (3) testing: increase in air permeability
The calculation formula of the increase value of air permeability for each of the separators prepared in examples 1 to 12 and comparative examples 1 to 5 was as follows:
the increase in air permeability is the air permeability value of the heat-treated separator of test 1-the air permeability value of the heat-treated separator of test 1.
The air permeability was measured using an air permeability tester (Asahi-Seiko, EGO1-65-2 MR).
And (4) testing: battery shutdown
For each of the separators prepared in examples 1 to 12 and comparative examples 1 to 5, lithium cobaltate (LiCoO) was used2) As the positive electrode, graphite was used as the negative electrode, an electrolyte containing LiPF 6 and the separator were used to prepare a coin cell. For examples 1-2, the coin cells were heated to 100 ℃ and held at 100 ℃ for 2 hours. For examples 3-12 and comparative examples 1-5, the coin cells were heated to 120 ℃ and held at 120 ℃ for 2 hours. Then, the button cell was subjected to a charge and discharge test. If the button cell can be charged or discharged, it indicates that the button cell is not turned off. Otherwise, the button cell is successfully switched off, i.e. it cannot be charged or discharged. The button cell which is shut down after heat treatment has higher safety than the button cell which can not be shut down after heat treatment.
TABLE 1 test results
As shown in table 1, the separators prepared in examples 1 to 10 maintained their dimensional stability at 120 ℃. The separators prepared in examples 11 to 12 maintained their dimensional stability at 105 ℃ but deformed at 120 ℃ because they did not contain inorganic materials in the coating layer. This indicates that the presence of the inorganic material in the coating layer can improve the heat resistance of the separator.
With respect to the increase in air permeability, the separators prepared in examples 1 to 12 had higher increase values of air permeability as compared to the separators prepared in comparative examples 1 to 5. The higher the increase in air permeability, the more ion flow channels in the membrane are blocked. Therefore, for the separators prepared in examples 1 to 12, ion current channels in the separators were more blocked after the heat treatment in test 1, compared to the separators prepared in comparative examples 1 to 5. The test results for cell shutdown shown in table 1 also confirm this conclusion.
Fig. 6 and 7 show SEM images of the separator prepared in example 1 before and after heat treatment in test 1. After the heat treatment, the PE particles melted as shown in fig. 6 and 7.