Wound electrode assembly, method of manufacturing the same, battery cell, battery, and power using device

Abstract

The application relates to the technical field of batteries, in particular to a wound electrode assembly, a preparation method thereof, a battery monomer, a battery and a power utilization device; the wound electrode assembly comprises a positive electrode, a negative electrode and a separator located between the positive electrode and the negative electrode; the separator comprises a base film and a bonding layer located on at least one side surface of the base film in the thickness direction; the porosity of the separator is 28%-34%; the deviation value of the bonding strength of any one circle of the separator in the wound electrode assembly and the bonding strength of other circles of the separator is less than or equal to 20%. Compared with the prior art, the porosity of the separator and the bonding strength of each circle of the separator in the electrode assembly are cooperatively designed, so that lithium ions can be rapidly transmitted in the electrode assembly, thereby effectively reducing the internal resistance of the battery monomer and improving the cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and more particularly to a wound electrode assembly, a preparation method thereof, a battery monomer, a battery and a power utilization device. BACKGROUND

[0002] The performance of a power battery monomer mainly includes core indexes such as energy density, power density, cycle performance, safety and environmental adaptability, wherein the cycle performance directly affects the endurance, service life and user cost of an electric vehicle; the better the cycle performance is, the slower the electrode material and electrolyte are consumed in the charging and discharging process of the battery monomer, and the slower the endurance mileage is attenuated.

[0003] The wound battery monomer is a sealed valve-regulated battery monomer formed by winding a positive electrode, a negative electrode and a separator through a winding process, and is mainly applied to fields such as automobile starting, military equipment, industrial equipment and medical devices. Because the production process is mature and the applicability is wide, the wound battery monomer occupies a dominant position in the field of power battery monomers. However, the cycle performance of the traditional wound battery monomer is not high, which restricts the further development of the wound battery monomer in the new energy field. Therefore, how to effectively improve the cycle performance of the wound battery monomer has become a technical problem to be solved by technical personnel in the field. SUMMARY

[0004] Therefore, the present application provides a wound electrode assembly, a preparation method thereof, a battery monomer, a battery and a power utilization device, which can make lithium ions rapidly transmit inside the electrode assembly by matching the porosity of the separator and the bonding strength of the separator of each coil of the electrode assembly, thereby reducing the internal resistance of the battery and improving the cycle performance.

[0005] In order to solve the above technical problems, the present application is implemented as follows:

[0006] According to one aspect of the present application, the present application provides a wound electrode assembly, comprising a positive electrode, a negative electrode and a separator located between the positive electrode and the negative electrode, the separator comprising a base film and a bonding layer located on at least one side surface of the base film in the thickness direction; the porosity of the separator is 28% to 34%; the deviation value of the bonding strength of any coil of the separator in the wound electrode assembly from the bonding strength of other coils of the separator is ≤20%.

[0007] In some embodiments, the bonding strength of any coil of the separator in the wound electrode assembly is 5N / m to 15N / m;

[0008] And / or, the air permeability value of the separator is ≤230s / 100cc;

[0009] And / or, the puncture resistance of the separator is ≥350gf.

[0010] In some embodiments, the thickness of the adhesive layer is 1-5 μm.

[0011] In some embodiments, the thickness of the base film is 3-14 μm.

[0012] According to another aspect of the present application, the present application provides a method for preparing a wound electrode assembly, comprising the following steps:

[0013] a) mixing an adhesive polymer, an adhesive emulsion and a solvent to obtain a slurry; coating the slurry on at least one side surface of a base film to form an adhesive layer after drying to obtain a separator; the adhesive temperature of the adhesive polymer is -25-25 °C, and the adhesive temperature of the adhesive emulsion is <-10 °C; the mass ratio of the adhesive polymer to the adhesive emulsion is (7-9):(1-3);

[0014] b) arranging the separator obtained in step a) between a positive electrode and a negative electrode, winding, and then pressing to obtain a wound electrode assembly.

[0015] In some embodiments of step a),

[0016] the adhesive polymer comprises a base and a modified group grafted on the base, the base comprises at least one of polyacrylate, polyvinylidene fluoride, ethylene-vinyl acetate copolymer, and the modified group is formed by a modified monomer with a glass transition temperature > 90 °C.

[0017] In some embodiments, the modified group comprises at least one of fluorostyrene group, acrylic acid group, maleic anhydride group, and glycidyl methacrylate group.

[0018] In some embodiments, the mass percentage of the modified group in the adhesive polymer is 8-15%.

[0019] In some embodiments of step a),

[0020] the micro-morphology of the adhesive polymer is microspheres, and the average particle size of the microspheres is 1-4 μm.

[0021] In some embodiments, the adhesive emulsion comprises at least one of polyacrylate emulsion, polyacrylonitrile emulsion, polyimide emulsion, polyethylene glycol emulsion, polydopamine emulsion, polyvinyl alcohol emulsion, and polyacrylic acid emulsion.

[0022] In some embodiments, the mixing temperature is 15-35 °C, the rotation speed is 100-1000 rpm, and the mixing time is 10-60 min.

[0023] And / or, the coating method is spraying.

[0024] And / or, the coating amount is 0.3g / m 2 1g / m 2 ;

[0025] And / or, the drying temperature is 35℃~60℃.

[0026] In some embodiments, the binding polymer is maleic anhydride modified ethylene-vinyl acetate copolymer, the binder emulsion is polyacrylate emulsion, and the mass ratio of the binding polymer and the binder emulsion is 8:2.

[0027] In some embodiments, in step b):

[0028] The pressing method is cold pressing, the cold pressing temperature is 15℃~25℃, the pressure is 5MPa~10MPa, and the time is 20s~30s.

[0029] In some embodiments, the air permeability of the cold-pressed separator is increased by ≤300s / 100cc compared with that of the separator before cold pressing.

[0030] And / or, the cold-pressed separator has a change rate of puncture resistance ≤5% compared with that of the separator before cold pressing.

[0031] And / or, the cold-pressed separator has a 140℃ heat shrinkage rate <2% compared with that of the separator before cold pressing.

[0032] According to another aspect of the present application, the present application provides a battery cell comprising the wound electrode assembly prepared by the preparation method described above.

[0033] According to another aspect of the present application, the present application provides a battery comprising the battery cell described above.

[0034] According to another aspect of the present application, the present application provides an electric device comprising the battery described above.

[0035] The technical solution of the present application has at least the following beneficial effects:

[0036] 1、The present application can make lithium ions rapidly transmit inside the electrode assembly by designing the porosity of the separator and the adhesion strength of the separator of each circle of the electrode assembly, thereby effectively reducing the internal resistance of the battery cell and improving the cycle performance.

[0037] 2、The application further improves the raw material selection and preparation process, on the premise of ensuring porosity, the bonding effect of the inner and outer rings of the electrode assembly is uniform: by introducing a specific bonding polymer into the separator bonding layer, the electrode sheet and the separator can be tightly bonded after cold pressing, and the problems of traditional pressing are effectively avoided (satisfying the bonding performance of the inner ring, the hole blocking of the outer ring separator caused by excessive temperature / overpressure, the decrease of porosity, or satisfying the bonding performance and porosity requirement of the outer ring, and the problem of insufficient bonding of the inner ring); on the other hand, the heat shrinkage of the separator is improved: in the specific bonding polymer, the high Tg (glass transition temperature) part can improve the heat shrinkage performance of the separator, and improve the safety performance of the separator and the battery monomer; and also improve the puncture resistance of the separator: the specific bonding polymer used in combination with the specific cold pressing process can prevent the crystalline region of the polymer in the separator from melting, ensure that the puncture resistance of the separator is high and the temperature is maintained, reduce the probability of internal short circuit of the separator, thereby improving the safety performance of the battery monomer in needle test, and also reducing the risk of heat shrinkage of the separator.

[0038] 3、The preparation method of the wound electrode assembly provided by the application has simple process, mild and easy-to-control conditions, low raw material and equipment cost, and wide application prospect.

[0039] Additional aspects and advantages of the application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0040] The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0041] Figure 1 SEM photo of the bonding polymer microspheres in Example 1 of the application.

[0042] Figure 2 Test schematic diagram of 140℃ heat shrinkage.

[0043] Through the above drawings, the specific embodiments of the application have been shown, and will be described in more detail hereinafter. These drawings and written description are not intended to limit the scope of the inventive concept in any way, but to illustrate the concept of the application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0044] The application will be further described below in conjunction with specific examples. It should be understood that these examples of the application are only used to illustrate the application and not to limit the scope of the application.

[0045] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the application. Any numeric range recited is intended to include all values from the lower value to the upper value, inclusive of both values, and to also include any value approximately or about the exact value.

[0046] In the description of the present application, "the same chemical composition" should be understood broadly, that is, the main components of both have the same chemical composition, or the chemical composition of both is basically the same, which can have errors within the range that can be understood by those skilled in the art and within the range that can be allowed in the art or contain impurities within the allowable range.

[0047] In the description of the present application, "A and / or B" can include any one of the cases of A alone, the case of B alone, and the case of A and B, where A and B are used only for example, and can be any technical feature connected by "and / or" in the present application.

[0048] If not specifically stated, "including" and "comprising" mentioned in the present application represent open type, and can also be closed type. For example, "including" and "comprising" can represent that other components not listed can also be included or contained, or can only include or contain the listed components.

[0049] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0050] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0051] If not specifically stated, all steps of the present application can be performed in sequence or randomly, and are preferably performed in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] The performance of the power battery cell mainly includes energy density, power density, cycle performance, safety, environmental adaptability and other core indicators. The cycle performance directly affects the endurance, service life and user cost of electric vehicles. The better the cycle performance, the slower the electrode material and electrolyte loss during charging and discharging, and the slower the endurance mileage decay.

[0053] The inventor of the present application has found that the cycle performance of a battery cell is affected by multiple factors, among which the internal resistance is an important one, and reducing the internal resistance can reduce the energy loss of the battery cell during charging and discharging, thereby slowing down the capacity attenuation of the battery cell and improving the cycle life. In order to reduce the internal resistance, some researchers increase the pressure, temperature and time during the hot pressing of the electrode assembly to improve the bonding strength, so that the electrode assembly is tightly bonded together, and some researchers increase the porosity of the separator to enable lithium ions to quickly pass through the pores of the separator and improve the transmission efficiency of lithium ions. However, neither of the above two technical solutions comprehensively considers the overall structure of the wound electrode assembly, so both of them have little effect on reducing the internal resistance.

[0054] On this basis, the inventor of the present application has found that by matching the porosity of the separator and the bonding strength of the separator of each coil of the electrode assembly, lithium ions can be quickly transmitted within the electrode assembly, thereby reducing the internal resistance of the battery cell and improving the cycle performance. Specifically, the present application adopts the following technical solutions:

[0055] According to one aspect of the present application, the present application provides a wound electrode assembly, comprising a positive electrode, a negative electrode and a separator located between the positive electrode and the negative electrode, the separator comprising a base film and a bonding layer located on at least one side surface of the base film in the thickness direction; the porosity of the separator is 28% to 34%; the deviation value of the bonding strength of any coil of the separator from the bonding strength of other coils of the separator is ≤20%.

[0056] In the specific embodiment of the present application, the separator of the wound electrode assembly is arranged between the positive electrode and the negative electrode; the separator comprises a base film and a bonding layer, wherein the base film can use a separator substrate well known to those skilled in the art, and the present application does not have special limitations on the type and source of the base film layer, such as a polyethylene (PE) base film, a polypropylene (PP) base film, etc. A ceramic layer can also be provided on the above-mentioned base film, and the present application does not have special limitations thereon. In the present application, the thickness of the base film is preferably 3 μm to 14 μm.

[0057] In the specific embodiment of the present application, the bonding layer is arranged on at least one side surface of the base film in the thickness direction, and is preferably arranged on both side surfaces of the base film in the thickness direction; on this basis, the positive electrode is connected to the separator through the bonding layer on one side surface of the base film, and the negative electrode is connected to the separator through the bonding layer on the other side surface of the base film, thereby ensuring that the positive electrode and the separator and the negative electrode and the separator can be bonded and connected through the bonding layer.

[0058] In the embodiment of the present application, the porosity of the separator is 28% to 34%; the deviation of the bonding strength of any one circle of the separator in the jelly-roll electrode assembly from the bonding strength of other circles of the separator is less than or equal to 20%. In the present application, the any one circle of the separator in the jelly-roll electrode assembly includes any one circle of all the circle layers from the innermost circle to the outermost circle, and other circles of the separator are other than the above, and on this basis, the deviation of the bonding strength of any one circle of the separator in the jelly-roll electrode assembly from the bonding strength of other circles of the separator is equal to (the maximum value of the bonding strength of all the circles of the separator - the minimum value of the bonding strength of all the circles of the separator) / the maximum value of the bonding strength of all the circles of the separator.

[0059] The above-mentioned porosity and bonding strength deviation value are synergistically matched, so that lithium ions can freely shuttle between the circle layer structures, effectively reducing the internal resistance; if the porosity of the separator is too large, the mechanical properties are poor, the separator structure is unstable, which can cause the internal resistance of the battery monomer to increase during the charging and discharging process, and the capacity of the battery monomer cannot be restored to the initial state, reducing the cycle performance, and if the porosity of the separator is too small, it will hinder the normal transmission of lithium ions, which is also not conducive to the reduction of internal resistance; and within the above-mentioned specific range of the porosity of the separator, the bonding strength value deviation between the circle layers is too large, which can cause the internal lithium ion transmission efficiency to present a difference, which is generally not conducive to the reduction of internal resistance.

[0060] In the embodiment of the present application, the bonding strength of any one circle of the separator in the jelly-roll electrode assembly is preferably 5 N / m to 15 N / m; if the bonding strength is too large, part of the bonding material can block the pores of the separator, reducing the porosity; if the bonding strength is too small, the bonding between the electrode sheet and the separator is not firm, which can increase the distance of lithium ion transmission, easily leading to an increase in internal resistance.

[0061] In the embodiment of the present application, the air permeability of the separator is less than or equal to 230 s / 100cc; if the air permeability is too large, the pores of the separator are blocked, affecting the transmission of lithium ions and increasing the internal resistance.

[0062] In the embodiment of the present application, the puncture resistance of the separator is greater than or equal to 350 gf; if the puncture resistance is too small, the short circuit probability of the separator increases, affecting the safety performance of the battery monomer, therefore, the puncture resistance needs to be designed to meet the above-mentioned requirements, to ensure the normal operation of the battery monomer, thereby ensuring the cycle performance of the battery monomer.

[0063] In the embodiment of the present application, the thickness of the bonding layer is preferably 1 μm to 5 μm; if the bonding layer is too thick, it can increase the transmission distance of lithium ions and increase the internal resistance; if the bonding layer is too thin, the compression ratio of the bonding layer after the electrode assembly is pressed is too small, affecting the bonding effect. In the preferred embodiment of the present application, the bonding layer is located on both sides of the base film along the thickness direction, to avoid ambiguity, the thickness of the bonding layer referred to here represents the thickness of the single-sided bonding layer rather than the total thickness of the two-sided bonding layers.

[0064] The positive electrode and the negative electrode are not particularly limited in the present application, and the conventional technical solutions of the positive electrode plate and the negative electrode plate known to those skilled in the art can be used.

[0065] In the embodiment of the present application, the positive electrode is specifically a positive electrode plate, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector in the thickness direction; wherein the positive electrode current collector can be a metal foil, a foamed metal or a composite current collector. For example, as a metal foil, silver surface treated aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrode, carbon or titanium, etc. can be used; the foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, etc.; the composite current collector can comprise a polymer material base layer and a metal layer, and the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0066] In the embodiment of the present application, the positive electrode active material layer comprises a positive electrode active material, and the present application does not have a particular limitation on the specific type of the positive electrode active material, and the active material known in the art that can be used for the positive electrode of a battery cell can be used, and those skilled in the art can select according to actual needs. Specifically, the positive electrode active material can include but is not limited to at least one of lithium transition metal oxides, olivine structure lithium-containing phosphates and their respective modified compounds; examples of lithium transition metal oxides can include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their modified compounds; examples of olivine structure lithium-containing phosphates can include but are not limited to at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon and their modified compounds. These materials can be obtained through commercial channels.

[0067] In the detailed description of the present application, the positive electrode active material layer can also generally include a positive electrode binder, a positive electrode conductive agent and other optional additives. As an example, the positive electrode binder can include at least one of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB); the positive electrode conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene and carbon nanofibers. These materials can all be obtained through commercial channels.

[0068] In the detailed description of the present application, the preparation method of the positive electrode tab adopts a method well known to those skilled in the art, i.e., first mixing the raw materials in a certain ratio in a solvent to prepare a positive electrode slurry, then coating the positive electrode slurry on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode tab can be obtained.

[0069] In the detailed description of the present application, the negative electrode is specifically a negative electrode tab, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector in the thickness direction; wherein the negative electrode current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, copper foil can be used; the composite current collector can include a high polymer material base layer and a metal layer formed on at least one surface of the high polymer material base material, and the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a high polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0070] In the detailed description of the present application, the negative electrode active material layer includes a negative electrode active material, and the present application does not have special limitations on the specific type of the negative electrode active material, and any active material known in the art that can be used for the negative electrode of a battery cell can be used, and those skilled in the art can select according to actual needs. Specifically: the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate, etc.; wherein the silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite and silicon alloy; the tin-based material can be selected from at least one of elemental tin, tin oxide compound and tin alloy. These materials can all be obtained through commercial channels.

[0071] In the detailed description of the present application, the negative active material layer can also generally include a negative electrode binder, a negative electrode conductive agent and other optional additives. As an example, the negative electrode binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS); the negative electrode conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene and carbon nanofibers; and the other optional additives can be, for example, a thickening agent such as carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na) and the like. These materials can all be obtained through commercial channels.

[0072] In the detailed description of the present application, the negative electrode sheet is prepared by first mixing the raw materials in a certain ratio in a solvent to obtain a negative electrode slurry, then coating the negative electrode slurry on a negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet is obtained.

[0073] The present application is directed to a wound electrode assembly, in which the above-mentioned positive electrode sheet, separator and negative electrode sheet are sequentially arranged with the separator placed between the positive electrode sheet and the negative electrode sheet, and then wound to form a wound structure. The shape of the wound electrode assembly can be cylindrical, flat or polygonal, etc.

[0074] In the detailed description of the present application, the wound electrode assembly is provided with a tab, which can guide the current out of the wound electrode assembly; the tab includes a positive tab and a negative tab.

[0075] According to another aspect of the present application, the present application provides a method for preparing a wound electrode assembly, comprising the following steps:

[0076] a) mixing a binder and a solvent to obtain a slurry; then coating the slurry on at least one side surface of a base film to form a bonding layer after drying, thereby obtaining a separator;

[0077] b) arranging the separator obtained in step a) between a positive electrode and a negative electrode, winding, and then pressing to obtain a wound electrode assembly.

[0078] The present application first mixes a binder and a solvent to obtain a slurry; then coats the slurry on at least one side surface of a base film to form a bonding layer after drying, thereby obtaining a separator; wherein the binder includes, but is not limited to, a bonding polymer and / or a binder emulsion known to those skilled in the art. In a preferred embodiment of the present application, the binder includes a bonding polymer and a binder emulsion; on this basis, the present application first mixes a bonding polymer, a binder emulsion and a solvent to obtain a slurry.

[0079] In the embodiment of the present application, the bonding temperature of the bonding polymer is -25℃ to 25℃, preferably -20℃ to -15℃; the bonding temperature mentioned in the present application refers to the lowest temperature that can achieve the bonding effect, which will not be repeated here. In the present application, the bonding polymer preferably comprises a base and a modified group grafted on the base, wherein the base preferably comprises at least one of polyacrylate, polyvinylidene fluoride (PVDF), ethylene-vinyl acetate copolymer (EVA), more preferably polyacrylate, polyvinylidene fluoride (PVDF) or ethylene-vinyl acetate copolymer (EVA); on this basis, the bonding polymer can be named as modified polyacrylate, modified PVDF, modified EVA according to the type of base.

[0080] In the embodiment of the present application, the modified group is formed by a modified monomer, and the glass transition temperature of the modified monomer is preferably > 90℃, and the high glass transition temperature part can improve the thermal shrinkage performance of the separator and improve the safety performance of the separator and the electrode assembly; on this basis, the modified group preferably comprises at least one of fluorostyrene group, acrylic acid group, maleic anhydride group, glycidyl methacrylate group, more preferably fluorostyrene group, acrylic acid group, maleic anhydride group or glycidyl methacrylate group.

[0081] In the embodiment of the present application, the mass percentage of the modified group in the bonding polymer is preferably 8% to 15%; specifically it can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% and the like. Too much modified monomer, poor bonding effect under cold pressure conditions; too little modified monomer, the separator is easy to self-bond.

[0082] In the preferred embodiment of the present application, the modified polyacrylate includes but is not limited to 2,3,4,5,6-pentafluorostyrene modified polyacrylate, 4-fluorostyrene modified polyacrylate and the like specific types; the modified PVDF includes but is not limited to acrylic acid modified PVDF, methacrylic acid modified PVDF, butyl acrylate modified PVDF and the like specific types; the modified EVA includes but is not limited to maleic anhydride modified EVA, glycidyl methacrylate modified EVA and the like specific types. The present application does not have special restrictions on the source of the above bonding polymers, and commercially available or self-made products known to those skilled in the art can be used.

[0083] In the most preferred embodiment of the present application, the bonding polymer is a maleic anhydride modified ethylene-vinyl acetate copolymer (maleic anhydride modified EVA); the anhydride group in the maleic anhydride monomer has high activity, which can significantly enhance the polarity of EVA, improve the ability of the bonding layer to absorb electrolyte, and help improve the cycle performance of the battery cell; the EVA backbone has good compatibility with the non-polar polyolefin (PP / PE base film), making the bonding of the bonding layer and the base film more stable.

[0084] In the detailed description of the present application, the micro-morphology of the bonding polymer is preferably microspheres; the use of microspherical morphology can make the slurry more easily dispersed and uniform, and the specific surface area of the microspherical bonding polymer is larger, which is more conducive to the wetting of the slurry on the surface of the base film, and the subsequent spray points do not aggregate and spread into a ring shape, making the bonding surface of the bonding layer larger and the bonding strength higher, which is beneficial to improving the cycle performance of the battery cell.

[0085] In the detailed description of the present application, the average particle size of the microspheres is preferably 1-4 μm; if the particle size is too large, the thickness of the slurry after drying by spraying is too high, resulting in an excessively thick separator, which is not conducive to the internal resistance; if the particle size is too small, the compression ratio after cold pressing is too small, affecting the improvement of the bonding strength.

[0086] In the detailed description of the present application, the bonding temperature of the binder emulsion is <-10℃; the binder emulsion preferably includes at least one of polyacrylate emulsion, polyacrylonitrile emulsion, polyimide emulsion, polyethylene glycol emulsion, polydopamine emulsion, polyvinyl alcohol emulsion, polyacrylic acid emulsion, and poly-n-butyl acrylate emulsion, and more preferably polyacrylate emulsion; it has good flexibility, making the bonding layer less likely to fall off powder and the bonding layer more stable. The present application does not have special restrictions on the source of the binder emulsion, and commercially available or self-made products known to those skilled in the art can be used.

[0087] In the detailed description of the present application, the mass ratio of the bonding polymer to the binder emulsion is (7-9):(1-3); specifically, it can be 7:3, 8:2, or 9:1. If the mass ratio of the bonding polymer to the binder emulsion is too large, the porosity of the separator after cold pressing is too high, affecting the internal resistance and cycle capacity retention rate of the electrode assembly; if the mass ratio is too small, the bonding of the bonding layer and the base film is poor.

[0088] In the preferred embodiment of the present application, the bonding polymer is a maleic anhydride modified ethylene-vinyl acetate copolymer, the binder emulsion is a polyacrylate emulsion, and the mass ratio of the bonding polymer to the binder emulsion is 8:2. On this basis, the maleic anhydride modified ethylene-vinyl acetate copolymer and the polyacrylate emulsion are used in a specific ratio, which has the best effect.

[0089] In a specific embodiment of the present invention, the solvent is preferably water, and deionized water, which is well known to those skilled in the art, can be used. The present invention does not have any special limitations on this. The purpose is to mix the bonding polymer and the adhesive emulsion evenly to obtain a slurry.

[0090] In a specific embodiment of the present invention, the mixing temperature is preferably 15℃~35℃, specifically 15℃, 20℃, 25℃, 30℃ or 35℃, etc.; the mixing speed is preferably 100rpm~1000rpm, specifically 100rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm or 1000rpm, etc.; the mixing time is preferably 10min~60min, specifically 10min, 20min, 30min, 40min, 50min or 60min, etc.

[0091] Subsequently, the present invention coats the slurry onto at least one side of the base membrane, and after drying, forms an adhesive layer to obtain a diaphragm.

[0092] In a specific embodiment of the present invention, the coating method is preferably spraying, thereby ensuring more uniform dispersion; the coating amount is preferably 0.3 g / m³. 2 ~1g / m 2 Specifically, it could be: 0.3g / m 2 0.4g / m 2 0.5g / m 2 0.6g / m 2 0.7g / m 2 0.8g / m 2 0.9g / m 2 or 1g / m 2 Etc. If the coating amount is too large, the adhesion strength between the diaphragm and the electrode will be too high; if the coating amount is too small, the adhesion strength will be insufficient.

[0093] In specific embodiments of the present invention, the present invention does not impose any special restrictions on the type and source of the base film, and any membrane substrate well known to those skilled in the art can be used; for example, it can be a polyethylene (PE) base film, a polypropylene (PP) base film, etc., and a ceramic layer (usually called a CCS layer, which contains ceramic particles, such as alumina) can also be provided on the above base film. The present invention does not impose any special restrictions on this.

[0094] In the embodiment of the present application, the drying temperature is preferably 35-60℃, and can be 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, etc. The drying time is adjusted according to the actual situation, so that the surface is dry. After drying, a bonding layer is formed on at least one side of the base film, thereby obtaining a separator. The thickness of the bonding layer is preferably 1-5μm.

[0095] After obtaining the separator, the obtained separator is arranged between the positive electrode and the negative electrode, and then is wound and pressed to obtain a wound electrode assembly. In the present application, the positive electrode and the negative electrode are the same as described in the above technical solution, and will not be described here.

[0096] The present application adopts a winding assembly method to form an initial electrode, and then is pressed to obtain a wound electrode assembly.

[0097] In the embodiment of the present application, the pressing method is preferably cold pressing treatment. The temperature of the cold pressing treatment is preferably 15-25℃, and can be 15℃, 20℃ or 25℃, etc. The pressure of the cold pressing treatment is preferably 5-10MPa, and can be 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa, etc. The time of the cold pressing treatment is preferably 20-30s, and can be 20s, 25s or 30s, etc. In the present application, whether the conventional hot pressing treatment or the preferred cold pressing treatment of the present application is used, the wound electrode assembly using the separator can meet the subsequent use requirements, and is further applied in the preparation of a battery monomer, and the performance of the obtained battery monomer meets the performance standards in the field. By using the preferred cold pressing treatment of the present application, better improvement effect can be achieved in cooperation with other elements such as a binder composition, that is, on the basis of meeting good and stable performance, the performance to be improved is mainly improved.

[0098] In the embodiment of the present application, the air permeability increment of the separator after cold pressing compared with that before cold pressing (after cold pressing-before cold pressing) is ≤300s / 100cc. In the present application, the air permeability of the separator before and after cold pressing will change, and the technical solution provided by the present application can ensure that the air permeability of the separator before and after cold pressing meets the normal operation of the battery monomer, while the adverse effects caused by the change are minimized.

[0099] In the embodiment of the present application, the change rate of the puncture resistance of the separator after cold pressing compared with that before cold pressing ((before cold pressing-after cold pressing) / before cold pressing) is ≤5%. In the present application, the puncture resistance of the separator before and after cold pressing will also change, and the technical solution provided by the present application can ensure that the puncture resistance of the separator before and after cold pressing meets the normal operation of the battery monomer, while the adverse effects caused by the change are minimized.

[0100] In the embodiment of the present application, the cold-pressed separator has a heat shrinkage rate of <2% at 140℃, compared with the separator before cold-pressing. In the present application, the separator before and after cold-pressing will generate heat shrinkage, and the technical solution provided by the present application can ensure that the separator before and after cold-pressing can meet the normal operation of the battery monomer, while the heat shrinkage rate is reduced to the maximum, thereby minimizing its impact.

[0101] The preparation method of the wound electrode assembly provided by the present application has simple process, mild and easy-to-control conditions, low raw material and equipment cost, and does not use organic solvents and other raw materials, is more environmentally friendly, and has a wide application prospect.

[0102] The present application further realizes the tight bonding of the separator and the electrode sheet at room temperature by pressure after winding the positive and negative electrodes with the above-mentioned mixed coating of the bonding polymer and the adhesive on the separator, and the porosity of the separator is within the required range, the bonding effect between the inner and outer rings of the separator and the electrode sheet is consistent, the internal resistance is effectively reduced, and the cycle life of the battery monomer is improved.

[0103] According to another aspect of the present application, the present application provides a battery monomer comprising the wound electrode assembly of the above technical solution or the wound electrode assembly prepared by the preparation method of the above technical solution. Therefore, the battery monomer has all the features and advantages of the wound electrode assembly of the above technical solution, which will not be described here. Specifically, the wound electrode assembly is made of a positive electrode, a negative electrode and a separator by a winding process.

[0104] In the embodiment of the present application, the number of wound electrode assemblies contained in the battery monomer can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0105] In the embodiment of the present application, the battery monomer further comprises an electrolyte. During the charging and discharging process of the battery monomer, active ions are embedded and extracted between the positive electrode and the negative electrode; the electrolyte plays a role in conducting ions between the positive electrode and the negative electrode; the separator is arranged between the positive electrode and the negative electrode, mainly playing a role in preventing the short circuit of the positive and negative electrodes, and at the same time allowing ions to pass through.

[0106] For the electrolyte, it plays a role in conducting ions between the positive electrode and the negative electrode. The present application does not have specific limitations on the type of the electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or full solid.

[0107] In the detailed description of the present application, the electrolyte adopts an electrolyte solution; the electrolyte solution comprises an electrolyte salt and a solvent; wherein the electrolyte salt preferably comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium boric oxalate, lithium difluorophosphoric oxalate, lithium tetrafluorophosphoric oxalate, and more preferably lithium hexafluorophosphate; and the solvent preferably comprises one or more of vinyl carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyrosulfone, methyl ethyl sulfone, diethyl sulfone, and more preferably vinyl carbonate and diethyl carbonate.

[0108] In the detailed description of the present application, the electrolyte solution preferably further comprises a film-forming additive, such as a negative electrode film-forming additive, a positive electrode film-forming additive, and can further comprise an additive capable of improving certain performance of the battery monomer, such as an additive capable of improving overcharge performance of the battery monomer, an additive capable of improving high-temperature or low-temperature performance of the battery monomer, and the like.

[0109] In the detailed description of the present application, the battery monomer can comprise an outer package, which can be used to package the above-mentioned wound electrode assembly and electrolyte. The outer package of the battery monomer can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like, and specifically, the hard shell can comprise a shell body and a cover plate, wherein the shell body can comprise a bottom plate and a side plate connected to the bottom plate, the bottom plate and the side plate being enclosed to form a receiving cavity, the shell body having an opening communicating with the receiving cavity, and the cover plate being capable of being arranged on the opening to close the receiving cavity, the electrode assembly being packaged in the above-mentioned receiving cavity, and the electrolyte being infiltrated in the electrode assembly; or can be a soft package, such as a bag-type soft package; the material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, and the like can be listed.

[0110] The present application does not have special restrictions on the shape of the battery monomer, which can be cylindrical, square or any other shape, and those skilled in the art can select according to the specific actual needs.

[0111] According to another aspect of the present application, the present application provides a battery comprising the battery monomer of the above technical solution. Therefore, the battery has all the features and advantages of the battery monomer of the above technical solution, which will not be described here.

[0112] In a specific embodiment of the present invention, the battery can be a battery module assembled from individual battery cells. The battery module can contain one or more battery cells, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In the battery module, the multiple battery cells can be arranged sequentially along the length of the battery module; of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells can be fixed using fasteners. The battery module may also include a housing with a receiving space, in which the multiple battery cells are received.

[0113] In the description of this invention, "a plurality of" means two or more.

[0114] In a specific embodiment of the present invention, the battery described above can also be a battery pack assembled from the battery modules. The battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack. Specifically, the battery pack may include a battery box and multiple battery modules disposed within the battery box; the battery box includes an upper box and a lower box, the upper box covering the lower box and forming a closed space for accommodating the battery modules. The multiple battery modules can be arranged in the battery box in any manner.

[0115] According to another aspect of the present invention, an electrical device is provided, comprising the battery described in the above-described technical solution. Thus, the electrical device possesses all the features and advantages of the battery described in the above-described technical solution, which will not be repeated here. Specifically, the battery can serve as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, and energy storage systems.

[0116] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0117] Example 1

[0118] S1: The binder polymer, binder emulsion, and water are mixed and stirred at 500 rpm for 30 minutes at room temperature (25°C) to obtain the first slurry. The binder polymer is maleic anhydride-modified EVA, wherein the glass transition temperature of the maleic anhydride monomer (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) is 140°C, the bonding temperature of the binder polymer is -15°C, and the average particle size is 2.5 μm. The binder emulsion is a polyacrylate emulsion with a bonding temperature of -25°C. The mass ratio of the binder polymer to the binder emulsion is 8:2.

[0119] The above-mentioned adhesive polymer was prepared by melt grafting. Maleic anhydride monomer, EVA, and initiator (dicumyl peroxide) were added to a high-speed mixer and stirred at 2000 rpm for 30 minutes at room temperature (25°C) until homogeneous. The mixture was then melt-extruded using a twin-screw extruder at 190°C. The mass ratio of maleic anhydride monomer, EVA, and initiator was 1.4:10:0.05. The product was maleic anhydride-modified EVA. SEM test results are shown below. Figure 1 As shown, the product has a microstructure of microspheres with an average particle size of 2.5 μm.

[0120] S2: The first slurry obtained in step S1 is sprayed onto the surface of the PE base film coated with the ceramic layer and the ceramic surface. After drying, an adhesive layer is formed to obtain a separator; wherein the thickness of the PE base film is 7μm, the thickness of the ceramic layer is 2μm, and the thickness of the adhesive layer is 3μm; the spraying amount is 0.5g / m 2 The drying method is oven drying, with an oven temperature of 40℃, a coating speed of 80m / min, and an oven length of 25m.

[0121] S3: The positive electrode, the separator obtained in step S2, and the negative electrode are stacked together, with the separator located between the positive and negative electrodes. After being wound, an initial electrode assembly is formed, and then cold-pressed (20°C, 8MPa, 25s) to obtain a wound electrode assembly.

[0122] Among them, the positive electrode: the current collector is aluminum foil, the positive electrode active material layer is positive electrode active material (lithium iron phosphate): positive electrode binder (PVDF): positive electrode conductive agent (50% carbon nanotubes: 50% SP) = 97:2:1.

[0123] Negative electrode: The current collector is copper foil, and the negative electrode active material layer is composed of negative electrode active material (graphite): negative electrode binder (PAA): CMC: negative electrode conductive agent (SP) = 96.5:1.5:1:1.

[0124] Preparation of the battery cell: the winding electrode assembly is placed in an aluminum shell, injected with electrolyte (solute LiPF6, solvent EC and DMC (mass ratio of EC and DMC is 3:7), solute content is 15%), and after packaging, formation, and capacity distribution, the battery cell is obtained.

[0125] Example 2

[0126] The preparation method provided in Example 1 is adopted, and the only difference is that in S1, the bonding polymer is replaced by 4-fluorostyrene modified polyacrylate instead of maleic anhydride modified EVA; wherein the glass transition temperature of the 4-fluorostyrene monomer (purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.) is 95°C, and the bonding temperature of the bonding polymer is -20°C.

[0127] The above bonding polymer preparation method: by emulsion grafting method, the initiator (ammonium persulfate) is added to the polyacrylate emulsion, heated in 70°C water bath, and the 4-fluorostyrene monomer is added while stirring, and the dropping is completed within 4h, wherein the mass ratio of 4-fluorostyrene, polyacrylate and initiator is 1.4:10:0.04, and the product is the bonding polymer; the product is tested, and the micro-morphology is microspheres, and the average particle size of the microspheres is 2.5μm.

[0128] Finally, the winding electrode assembly is obtained.

[0129] Example 3

[0130] The preparation method provided in Example 1 is adopted, and the only difference is that in S1, the mass ratio of the bonding polymer to the binder emulsion is 7:3. Finally, the winding electrode assembly is obtained.

[0131] Example 4

[0132] The preparation method provided in Example 1 is adopted, and the only difference is that in S1, the mass ratio of the bonding polymer to the binder emulsion is 9:1. Finally, the winding electrode assembly is obtained.

[0133] Example 5

[0134] The preparation method provided in Example 1 is adopted, and the only difference is that in S1, the average particle size of the bonding polymer microspheres is 4μm. Finally, the winding electrode assembly is obtained.

[0135] Example 6

[0136] The preparation method provided in Example 1 is adopted, and the only difference is that in S1, the average particle size of the bonding polymer microspheres is 1μm. Finally, the winding electrode assembly is obtained.

[0137] Example 7

[0138] The preparation method provided in Example 1 is adopted, and the only difference is that in S2, the thickness of the adhesive layer is 5 μm. Finally, a wound electrode assembly is obtained.

[0139] Example 8

[0140] The preparation method provided in Example 1 is adopted, and the only difference is that in S2, the thickness of the adhesive layer is 1 μm. Finally, a wound electrode assembly is obtained.

[0141] Example 9

[0142] The preparation method provided in Example 1 is adopted, and the difference includes that in S1, the conventional PVDF (adhesion temperature is 140 ℃, and average particle size is 7.5 μm) is used instead of the adhesive polymer; in S3, after winding, the initial electrode assembly is formed, and then 70 ℃ low-temperature preheating is performed for 20 min, and then hot pressing (hot pressing temperature is 90 ℃, pressure is 5 MPa, and hot pressing time is 10 s) is performed. Finally, a wound electrode assembly is obtained.

[0143] Example 10

[0144] The preparation method provided in Example 1 is adopted, and the only difference is that in S1, the adhesive emulsion is replaced by n-butyl acrylate-acrylic acid copolymer adhesive emulsion, and the adhesion temperature is -15 ℃. Finally, a wound electrode assembly is obtained.

[0145] Comparative Example 1

[0146] The preparation method provided in Example 1 is adopted, and the difference is that the separator is replaced by a separator without an adhesive layer. Finally, a wound electrode assembly is obtained.

[0147] Comparative Example 2

[0148] The preparation method provided in Example 1 is adopted, and the difference is that the adhesive layer raw material is replaced by 10 parts of adhesive emulsion, and no adhesive polymer is added. Finally, a wound electrode assembly is obtained.

[0149] In addition, the pressing mode can adopt hot pressing: the initial electrode assembly is formed and then hot pressing (hot pressing temperature is 90 ℃, pressure is 5 MPa, and hot pressing time is 10 s) is performed. Finally, a wound electrode assembly is obtained.

[0150] Comparative Example 3

[0151] The preparation method provided in Example 1 is adopted, and the difference is that the adhesive polymer is replaced by hydroxymethyl acrylamide modified polyacrylate, and the adhesion temperature of the adhesive polymer is 50 ℃. Finally, a wound electrode assembly is obtained.

[0152] In addition, the pressing method can adopt hot pressing: the initial electrode assembly is formed and then hot pressed (hot pressing temperature is 90℃, pressure is 5MPa, and hot pressing time is 10s). Finally, the wound electrode assembly is obtained.

[0153] Comparative Example 4

[0154] The preparation method provided in Example 1 is adopted, except that the mass ratio of the binding polymer to the binder emulsion is 9.5:0.5. Finally, the wound electrode assembly is obtained.

[0155] Comparative Example 5

[0156] The preparation method provided in Example 1 is adopted, except that the mass ratio of the binding polymer to the binder emulsion is 6:4. Finally, the wound electrode assembly is obtained.

[0157] The parameters of the wound electrode assemblies provided in the above examples and comparative examples are shown in Tables 1-3 below.

[0158] Table 1: Adhesion strength of the separator to the electrode tab after hot / cold pressing of the thick wound core (30 turns in total)

[0159]

[0160] Test method: The coated separator is wound together with the positive and negative electrode tabs by a winding machine, and then hot or cold pressed, and the 180° adhesion strength of the electrode tab and the separator is tested by a universal testing machine.

[0161] Table 2: Porosity of the separator (after pressing)

[0162]

[0163] Test method: The mass difference of the separator before and after absorbing liquid n-hexadecane is measured by the liquid absorption method, and the volume of the absorbed liquid is calculated by combining the density of n-hexadecane. The porosity can be obtained by dividing the geometric volume of the separator.

[0164] Table 3: Comparison of the air permeability value and thermal shrinkage performance of the separator after hot / cold pressing of the wound core

[0165]

[0166] Test method:

[0167] ① Air permeability value: The air permeability value of the separator before and after pressing is tested by using an air permeability tester.

[0168] ② Puncture strength of the separator: An electronic tensile testing machine is used to fix the separator in a ring clamp, a spherical needle with a diameter of 1mm is used to puncture the separator sample at a speed of 100mm / min, and the maximum puncture strength during the puncture process is recorded.

[0169] ③ 140℃ heat shrinkage: refer to Figure 2 The separator was cut into a sample with a size of 10 cm x 10 cm, clamped with A4 paper, and placed in the sample after the oven was heated to 140°C for 1 h. The length of the sample in the MD direction after baking was tested, and the heat shrinkage rate was (MD direction length before baking - MD direction length after baking) / MD direction length before baking. The MD direction is the winding direction of the separator of the electrode assembly, and the TD direction is the width direction of the separator of the electrode assembly.

[0170] The wound electrode assembly provided by each of the above examples and comparative examples was further made into a battery monomer for subsequent performance tests, and the preparation method was as follows:

[0171] The wound electrode assembly was placed in an aluminum shell, and an electrolyte (solute LiPF6, solvent EC and DMC (mass ratio of EC and DMC 3:7), solute content 15%) was injected. After packaging, formation and capacity distribution, a battery monomer was obtained.

[0172] Performance test:

[0173] ① Battery monomer fast charging surface temperature rise test method: at 25°C, the prepared battery monomer was placed for 30 min, then charged to 3.65V at 4C rate constant current, and the surface temperature change of the battery monomer was monitored.

[0174] ② Battery monomer DCR test method: at 25°C, the prepared battery monomer was placed for 30 min, charged to 3.65V at 1 / 2C constant current, and then discharged to 50% SOC at 1C constant current. After standing for 60 min, discharge at 2C current for 10 s, the obtained is the resistance value at 25°C, 50% SOC, 2C discharge for 10 s.

[0175] ③ Battery monomer cycle capacity retention rate: the battery monomer was cycled at 25°C according to 1CC / 1DC rate for 1000 cycles, and the ratio of the remaining capacity to the initial capacity was calculated, that is, the capacity retention rate of the battery monomer was obtained.

[0176] The test results are shown in Table 4 below.

[0177] Table 4 Battery monomer fast charging temperature rise, battery monomer internal resistance, and cycle life effect data table

[0178]

[0179] From the above experimental data, it can be seen that the adhesion layer slurry of the separator coated by mixing the adhesive polymer and the binder emulsion in Examples 1-8 has small heat shrinkage, the separator has strong adhesion effect on the electrode sheet after the electrode assembly is wound and cold-pressed, and the adhesion effect is uniform from the outer ring to the inner ring of the electrode assembly; at the same time, the air permeability and the puncture strength of the separator change little before and after cold-pressing, and the porosity of the inner and outer rings of the separator is within a certain range; on this basis, the temperature rise of the battery monomer under fast charging is small, and the internal resistance of the battery monomer is low; in addition, cold-pressing can effectively avoid the stress release of the electrode assembly after hot-pressing, the thickness change of the electrode assembly before and after hot-pressing, the wrinkling of the electrode sheet, and the influence on the interface, thereby improving the long-term cycle life of the battery monomer. In Example 9, the internal temperature of the electrode assembly is uniformly raised in advance by low-temperature preheating, and the adhesion of the inner and outer rings of the electrode assembly can reach good effect after hot-pressing in a short time, and the air permeability increment and the porosity of the separator after pressing are not high; however, the preheating process has high energy consumption and large equipment floor space. In Comparative Example 1, the electrode assembly wound by the separator without coating the adhesion layer is pressed, and the adhesion strength of the separator to the electrode sheet is zero, the internal resistance of the battery monomer is large, and the capacity attenuation is fast. In Comparative Example 2, the separator only uses the binder emulsion, and the adhesion strength effect is good under cold-pressing and hot-pressing, but the air permeability increment of the separator after pressing is large, the internal resistance of the battery monomer is high, and the cycle life retention rate of the battery monomer is low. In Comparative Example 3, the modified polymer with a high adhesion temperature is used, and the adhesion strength of the separator to the electrode sheet is weak under cold-pressing. In Comparative Examples 4 and 5, the ratio of the adhesive polymer to the binder emulsion exceeds the preferred range, the adhesion effect of the separator to the electrode sheet is poor, the lithium ion transmission resistance is large, the internal resistance of the battery monomer is high, and the long-term cycle life of the battery monomer is affected.

[0180] The part of the present application not described in detail is the technology known to those skilled in the art.

[0181] The basic principles of the present application are described above in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects, etc. mentioned in the present application are only examples and not limitations, and these advantages, advantages, effects, etc. cannot be considered as the must-have of each embodiment of the present application. In addition, the above-mentioned specific details are only for the purpose of example and for the purpose of understanding, and are not limited to the must-use of the above-mentioned specific details to realize the present application.

[0182] In the above description of the specification, the description referring to the terms "one embodiment", "another embodiment", and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment are included in at least one embodiment of the present application. In the specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples, without contradiction. In addition, it should be noted that in the specification, the terms "first", "second" are for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A wound electrode assembly, characterized by, The separator comprises a positive electrode, a negative electrode and a separator located between the positive electrode and the negative electrode, the separator comprises a base film and a bonding layer located on at least one side surface of the base film along the thickness direction; the porosity of the separator is 28% to 34%; the bonding strength deviation value of any one circle of the separator in the wound electrode assembly and the bonding strength of other circles of the separator is ≤20%; The bonding layer comprises a bonding polymer and is formed by cold pressing; the bonding polymer comprises a base body and a modified group grafted on the base body, the base body comprises at least one of polyacrylate, polyvinylidene fluoride and ethylene-vinyl acetate copolymer, and the modified group comprises at least one of fluorostyrene group, acrylic acid group, maleic anhydride group and glycidyl methacrylate group.

2. The jellyroll electrode assembly according to claim 1, characterized by The bonding strength of any one circle of the separator in the wound electrode assembly is 5 N / m to 15 N / m; And / or, the air permeability value of the separator is ≤230 s / 100cc; And / or, the puncture resistance of the separator is ≥350 gf.

3. The jellyroll electrode assembly according to claim 1, characterized by The thickness of the bonding layer is 1 μm to 5 μm; And / or, the thickness of the base film is 3 μm to 14 μm.

4. The jellyroll electrode assembly according to claim 1, characterized by The modified group is formed by a modified monomer, and the glass transition temperature of the modified monomer is >90℃.

5. The jellyroll electrode assembly according to claim 1, characterized by The mass percentage of the modified group in the bonding polymer is 8% to 15%.

6. A method of producing the jelly-roll electrode assembly according to any one of claims 1 to 5, characterized by, The method comprises the following steps: a) mixing a bonding polymer, a binder emulsion and a solvent to obtain a slurry; then coating the slurry on at least one side surface of a base film to form a bonding layer after drying, thereby obtaining a separator; The bonding temperature of the bonding polymer is -25℃ to 25℃, and the bonding temperature of the binder emulsion is <-10℃; the mass ratio of the bonding polymer to the binder emulsion is (7 to 9):(1 to 3); b) arranging the separator obtained in step a) between a positive electrode and a negative electrode, winding and then pressing to obtain a wound electrode assembly.

7. The preparation method according to claim 6, characterized in that, In step a): The micro-morphology of the bonding polymer is microspheres; the average particle size of the microspheres is 1 μm to 4 μm; And / or, the binder emulsion comprises at least one of polyacrylate emulsion, polyacrylonitrile emulsion, polyimide emulsion, polyethylene glycol emulsion, polydopamine emulsion, polyvinyl alcohol emulsion and polyacrylic acid emulsion; And / or, the mixing temperature is 15℃ to 35℃, the rotation speed is 100 rpm to 1000 rpm, and the time is 10 min to 60 min; And / or, the coating mode is spraying; and / or the amount of the coating is 0.3 g / m 2 1 g / m 2 ; And / or, the drying temperature is 35℃ to 60℃; And / or, the bonding polymer is maleic anhydride modified ethylene-vinyl acetate copolymer, the binder emulsion is polyacrylate emulsion, and the mass ratio of the bonding polymer to the binder emulsion is 8:

2.

8. The preparation method according to claim 6, characterized in that, In step b): The pressing mode is cold pressing; the cold pressing temperature is 15℃ to 25℃, the pressure is 5 MPa to 10 MPa, and the time is 20 s to 30 s.

9. The production method according to claim 8, characterized by, The air permeability value increment of the separator after cold pressing compared with the separator before cold pressing is ≤300 s / 100cc; And / or, the puncture resistance change rate of the separator after cold pressing compared with the separator before cold pressing is ≤5%; And / or, the puncture resistance change rate of the separator after cold pressing compared with the separator before cold pressing is ≤5%. And / or, the cold-pressed separator has a 140℃ heat shrinkage rate of <2% compared to the cold-pressed separator.

10. A battery cell characterized by, The jelly-roll type electrode assembly prepared by the preparation method according to any one of claims 6 to 9.

11. A battery, characterized by The battery cell according to claim 10.

12. An electrical device, characterized by The battery according to claim 11.

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