CN117791040A

CN117791040A - Separator, secondary battery, and electronic device

Info

Publication number: CN117791040A
Application number: CN202311734336.6A
Authority: CN
Inventors: 曾观音
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2023-12-15
Filing date: 2023-12-15
Publication date: 2024-03-29

Abstract

The application discloses barrier film, secondary cell and electronic equipment, the barrier film includes the base film and sets up the polymer particle layer of at least one surface of base film, the polymer particle layer includes the polymer granule, the shell of polymer granule includes by monomer I, monomer II and monomer III through the first polymer of polymerization reaction formation, monomer I includes methacrylate monomer, monomer I's glass transition temperature is 8-80 ℃, monomer II includes at least one of acrylate monomer, acrylic acid alcohol ester monomer, acrylic acid monomer, monomer III includes the acrylonitrile. The application selects the proper monomer I, monomer II and monomer III to carry out copolymerization reaction so as to realize that electrolyte wettability between the pole piece and the isolating film interface is improved and high adhesion between the isolating film and the pole piece is also considered.

Description

Separator, secondary battery, and electronic device

Technical Field

The application relates to the technical field of batteries, in particular to a separation film, a secondary battery and electronic equipment.

Background

The soft package battery core is light by virtue of the self packaging material, and has the advantage of natural high energy density. However, the aluminum plastic film of the outer package of the soft package battery core has no binding force, so the high-adhesion isolating film is needed to be used for adhering the pole pieces and the high-adhesion isolating film together, so that the pole pieces are bound to be free from being scattered and deformed, and the strength is provided for the battery core. Meanwhile, the high-adhesion bound bare cell can reduce the relative thickness of the bare cell and improve the volume energy density. However, the high adhesion between the pole piece and the isolating membrane can lead to poor electrolyte infiltration between the pole piece and the isolating membrane interface, and the electrolyte is insufficient in the circulation process easily, so that the circulation water jump phenomenon occurs in the later period of circulation.

Disclosure of Invention

In view of this, the present application provides a barrier film, a secondary battery, and an electronic device, where the barrier film has high adhesion to a pole piece and can also enhance electrolyte wettability between the pole piece and the barrier film interface, and the barrier film is disposed in the secondary battery, which is advantageous for enhancing high temperature performance and cycle performance of the secondary battery.

In a first aspect, the present application provides a barrier film, the barrier film includes a base film and a polymer particle layer disposed on at least one side surface of the base film, the polymer particle layer includes polymer particles, a shell of the polymer particles includes a first polymer formed by polymerization reaction of a monomer I, a monomer II and a monomer III, the monomer I includes a methacrylate monomer or styrene, a glass transition temperature of the monomer I is 8-80 ℃, and an addition of the monomer I is used to ensure that the barrier film exerts a bonding effect with a pole piece at a certain temperature. The monomer II comprises at least one of acrylic ester monomer, acrylic alcohol ester monomer and acrylic monomer, and the addition of the monomer II is used for ensuring that the shell of the polymer particles is softened and fixed with the base film at the early stage (less than 60 ℃) of the formation stage, thereby being beneficial to enhancing the binding property between the diaphragm and the pole piece. Meanwhile, polymerization of the monomer I and the monomer II is beneficial to improving the cohesiveness between the polymer particle layer and the pole piece, so that the cohesive strength between the pole piece and the isolating film is further enhanced, and the monomer III comprises acrylonitrile. The application selects a proper amount of monomer III, monomer I and monomer II to polymerize, so that the affinity of the polymer particle layer to electrolyte is improved while the bonding strength is ensured, and the electrolyte wettability between the electrode plate and the isolating membrane interface is further improved.

In this application, at first carry out the polymerization through selecting suitable kind and the monomer of content ratio for realize playing the bonding efficiency at different stages, further promote the binding power between barrier film and the pole piece, do benefit to the volume energy density who improves the electric core, secondly, still add appropriate amount of monomer III that has polar group in the polymerization, monomer III with monomer I with monomer II's copolymerization can be in compromise barrier film and pole piece high bonding the while further promote electrolyte wettability between barrier film and the pole piece. Therefore, the polymer particles can realize the fixation between the polymer particle layer and the base film at the early stage of the formation stage, can realize the high adhesion between the polymer particle layer and the pole piece at the later stage (60-105 ℃) of the formation stage, are beneficial to improving the volume energy density of the battery core, and can also improve the electrolyte wettability between the pole piece and the isolation film interface while considering the high adhesion due to the fact that a proper amount of monomer III participates in the copolymerization together with a monomer II which plays a role in high adhesion and a monomer I which plays a role in functionality, so that the circulating water jump of the battery core at the later stage of circulation is avoided.

In some embodiments, the monomer I is selected from butyl methacrylate and/or isobutyl methacrylate, with a glass transition temperature of 20 to 53 ℃. The butyl methacrylate and/or the isobutyl methacrylate is more favorable for ensuring the processability of the isolating film, namely, the adhesive property between the isolating film and the pole piece is re-generated at the later stage of the formation stage.

In some embodiments, the monomer II is selected from at least one of isobutyl acrylate, isooctyl acrylate, ethylene glycol dimethacrylate, methacrylic acid, or acrylic acid. When the monomer II and the monomer I are polymerized, on one hand, the fixation between the polymer particle layer and the base film in the early stage of the formation stage can be realized, and on the other hand, the high adhesion between the isolation film and the pole piece in the later stage of the formation stage is facilitated through the polymerization reaction of the monomer I and the monomer II, so that the volume energy density of the soft-package battery cell is further improved.

In some embodiments, the first polymer has a number average molecular weight of 15 to 30 ten thousand. At this time, the high adhesion and high infiltration effects of the polymer particles are more favorably exerted.

In some embodiments, the mass ratio of the monomer I, the monomer II, and the monomer III is (0.5-1): 2-2.5): 0.3-0.6. When the mass ratio of the monomer I to the monomer II to the monomer III is in the range, the adhesion between the pole piece and the isolating film is guaranteed at the later stage of the formation stage, and meanwhile, the wettability between the pole piece and the interface of the isolating film can be remarkably improved, namely, the two-way improvement of the wettability and the volume energy density can be realized while the strength of the battery cell is guaranteed.

In some embodiments, the inner core of the polymer particle includes a second polymer formed by polymerization reaction of a monomer IV and a monomer V, the monomer IV includes a styrene monomer and/or an acrylic monomer, the glass transition temperature of the monomer IV is 105 ℃ to 120 ℃, the monomer IV is used for providing mechanical support for the polymer particle, and the polymer particle can maintain the integrity of the particle morphology under the formation condition of high temperature and high pressure (80 ℃ to 90 ℃ and 1Mpa to 2 Mpa), is not easy to collapse and plug holes, and ensures the internal resistance of the battery cell to be in a proper range. The monomer V comprises butadiene, and the mass ratio of the monomer IV to the monomer V is 1 (1-1.2).

In some embodiments, the mass percent of the polymer particles is 80wt% to 90wt%, based on the mass of the layer of polymer particles. At this time, the high adhesion between the isolating film and the pole piece is more facilitated, and the wettability between the pole piece and the isolating film is more facilitated to be improved. Preferably, the mass percentage of the polymer particles is 80wt% to 85wt%.

In some embodiments, the polymer particle layer further comprises a functional substance, the weight percent of the functional substance being 1wt% to 10wt% based on the mass of the polymer particle layer. Preferably, the mass percentage of the functional substance is 5-10wt%. The functional material is used to achieve bonding between the polymer particles.

In some embodiments, the polymer particles have an average particle size of 0.5nm to 1.2nm. Preferably, the polymer particles have an average particle diameter of 0.7nm to 0.9nm.

In some embodiments, the thickness of the release film is 8.5 μm to 9.0 μm.

In some embodiments, the mass percent of the first polymer is 20wt% to 40wt% and the mass percent of the second polymer is 60wt% to 80wt% based on the mass of the polymer particles. At the moment, the cohesiveness and wettability between the pole piece and the isolating film are improved, and the internal resistance of the battery cell is regulated and controlled properly. Preferably, the mass percentage of the first polymer is 30wt% to 40wt%, and the mass percentage of the second polymer is 60wt% to 70wt%.

In some embodiments, the separator is disposed after the secondary battery is subjected to the formation process, and the internal resistance of the secondary battery is 8 Ω to 16Ω, preferably 9 Ω to 15Ω. The adhesive force between the isolating film and the pole piece is 6N to 15N. Preferably, the adhesive force between the isolating film and the pole piece is 12N to 15N.

In a second aspect, the present application provides a secondary battery comprising a wound cell comprising a pole piece and the above-described separator, the surface of the pole piece being provided with an embossed area, at least part of the embossed area being provided in a corner region of the wound cell. According to the battery cell, the embossed area is formed on the surface of the pole piece, the pole piece after embossing and the isolating film are wound to form the bare battery cell, the bare battery cell is flattened under the action of high temperature and high pressure in the formation process, so that the thickness of the battery cell is not influenced, the energy density cannot be reduced, the ink (embossing) in the corner area is still kept, the ink in the corner can promote the liquid retention amount, and corner black spots and corner lithium precipitation caused by corner extrusion can be remarkably improved. The main body region refers to a straight section of the winding type battery cell, and the corner region refers to a bending section of the winding type battery cell.

In some embodiments, the pole piece comprises a first area and a second area along the length direction of the pole piece, the first area is a single-sided cloth area, the second area is a double-sided coating area, the coating surface of the first area is provided with a first embossing, and the first embossing is formed by sequentially applying 0.3 Mpa-0.4 Mpa force to the pole piece through a plurality of spherical protrusions with the particle size of 1.0 mm-5 mm. The coating surfaces on two sides of the second area are respectively provided with a second embossing, and the second embossing is formed by sequentially applying 0.3 Mpa-0.4M acting force to the polar plate through a plurality of spherical bulges with the particle size of 5.0 mm-10 mm. This application sets up different knurlings in the different regions on pole piece surface, through first knurling with the cooperation of second knurling for realize the promotion of winding type electricity core corner region department liquid retention ability.

In some embodiments, the first embossment has an embossment depth-to-diameter ratio in the range of 1 (0.5-1), the second embossment has an embossment depth-to-diameter ratio in the range of 1 (0.2-0.8), and the first and second regions have an area ratio of 1 (6-12). Therefore, a space for effectively storing electrolyte can be formed in the corner region of the winding type battery cell, and the problems of black spots at the corner and lithium precipitation at the corner caused by extrusion in the corner region are remarkably solved.

In a third aspect, the present application provides an electronic device comprising the secondary battery described above.

The application provides a barrier film, secondary cell and electronic equipment, polymer particle layer on barrier film surface contains polymer particle, polymer particle has core-shell structure, polymer particle's shell is used for realizing good infiltration and high bonding between barrier film and the pole piece, polymer particle's nuclear is used for providing mechanical support to make polymer particle can keep the integrality of granule topography under the formation condition of high temperature high pressure. The isolating film is configured in the secondary battery, so that the high-temperature performance and the cycle performance of the secondary battery can be improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic view of a part of a winding type battery cell in a secondary battery of the present application;

FIG. 2 is a schematic view of the structure of the separator of the present application when bonded to a pole piece;

FIG. 3 is a schematic illustration of embossed area distribution of a pole piece of the present application;

fig. 4 is a graph of the adhesion test of the examples of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.

At present, the high-adhesion water-based adhesive layer can realize the high adhesion of the isolating film and the pole piece, but also can bring the problem of poor electrolyte infiltration, the high-adhesion isolating film is very tightly attached to the pole piece, so that electrolyte is difficult to enter, the battery cell at the later cycle stage can generate circulating water jump due to lack of electrolyte, the internal resistance is increased, and the internal expression forms are black spots and lithium precipitation at the anode interface.

In order to solve the technical problem, the application provides a separation membrane, which has high bonding performance with a pole piece, and particularly can improve the infiltration performance of electrolyte.

Secondary battery

Referring to fig. 1, the present application provides a secondary battery including a winding type cell 110, the winding type cell 110 including a separator 101, a positive electrode tab 102, and a negative electrode tab, the positive electrode tab 102, the separator 101, and the negative electrode tab being sequentially laminated and wound to form the winding type cell 110, the winding type cell 110 including a bent corner region 111 and a flat body region 112, wherein the corner region 111 is a region covered with a start point a of a bent segment (a position where a flat segment starts to a bent segment) to an end point B of the bent segment (a position where a straight segment starts to be bent Duan Xiangping), and the corner region in another portion not shown in fig. 1 may be similarly described above.

Isolation film

Referring to fig. 2, the separator 101 includes a base film 11 and a polymer particle layer 12 disposed on at least one side surface of the base film 11, when the positive electrode sheet 102, the separator 101 and the negative electrode sheet are stacked, the polymer particle layer 12 is attached to an active material layer of the positive electrode sheet 102, and when the polymer particle layers 12 are disposed on both sides of the base film 11, when the positive electrode sheet 102, the separator 101 and the negative electrode sheet are stacked, the polymer particle layer 12 is attached to an active material layer of the positive electrode sheet 102 and an active material layer of the negative electrode sheet. In fig. 2, an active material layer is disposed on a surface of the spacer 101 facing the Al foil, one side of the active material layer is bonded to the Al foil, and the other side of the active material layer is bonded to the polymer particle layer 12. The polymer particle layer 12 includes polymer particles 121, the polymer particles 121 have a core-shell structure, and the shell of the polymer particles 121 includes a first polymer formed by polymerizing a monomer I, a monomer II, and a monomer III. The monomer I comprises a methacrylate monomer, the glass transition temperature of the monomer I is 60-105 ℃, the monomer II comprises at least one of an acrylate monomer, an acrylic alcohol ester monomer and an acrylic monomer, and the monomer III comprises acrylonitrile.

Illustratively, the glass transition temperature of the monomer I is 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, or a range of any two values recited above.

In some embodiments, the monomer I is selected from methyl methacrylate and/or isobutyl methacrylate. Specifically, in some examples, the monomer I is methyl methacrylate, in other examples, the monomer I is isobutyl methacrylate, in other examples, the monomer I includes both methyl methacrylate and isobutyl methacrylate.

In some embodiments, the monomer II is selected from at least one of isobutyl acrylate, isooctyl acrylate, ethylene glycol dimethacrylate, methacrylic acid, or acrylic acid.

In some embodiments, the first polymer has a number average molecular weight of 15 to 30 tens of thousands. Illustratively, the first polymer has a number average molecular weight in the range of 15 ten thousand, 18 ten thousand, 20 ten thousand, 23 ten thousand, 25 ten thousand, 28 ten thousand, 30 ten thousand, or any two of the values recited above.

In some embodiments, the mass ratio of the monomer I, the monomer II, and the monomer III is (0.5-1): 2-2.5): 0.3-0.6.

In some embodiments, the inner core of the polymer particle comprises a second polymer formed by polymerization of monomer IV and monomer V, wherein monomer IV comprises a styrenic monomer and/or an acrylic monomer, the glass transition temperature of monomer IV is 105 ℃ to 120 ℃, monomer V comprises butadiene, and the mass ratio of monomer IV to monomer V is 1 (1) to 1.2.

Illustratively, the glass transition temperature of the monomer IV is 105 ℃, 108 ℃, 110 ℃, 113 ℃, 115 ℃, 118 ℃, 120 ℃, or a range of any two values recited above.

In some embodiments, the mass percent of the polymer particles is 80wt% to 90wt%, based on the mass of the layer of polymer particles. Illustratively, the polymer particles are present in an amount of 80wt%, 83wt%, 85wt%, 88wt%, 90wt% or a range of any two of the foregoing values.

In some embodiments, the polymer particles have an average particle size of 0.5nm to 1.2nm. Illustratively, the polymer particles have an average particle size of 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1.0nm, 1.2nm, or a range of any two values recited above.

In some embodiments, the thickness of the release film is 8.5 μm to 9.0 μm. Illustratively, the thickness of the release film is 8.5 μm, 8.6 μm, 8.7 μm, 8.8 μm, 8.9 μm, 9.0 μm, or a range of any two values described above.

In some embodiments, the mass percent of the first polymer is 20wt% to 40wt% and the mass percent of the second polymer is 60t% to 80wt%, based on the mass of the polymer particles. Illustratively, the first polymer is present in an amount of 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or a range of any two of the foregoing values. Illustratively, the second polymer is present in a mass percent of 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, or a range of any two of the foregoing values.

In some embodiments, the polymer particle layer further comprises a functional substance comprising styrene-butadiene rubber and/or acrylic acid, the polymer particles being 80wt% to 90wt% and the functional substance being 1wt% to 10wt% based on the mass of the polymer particle layer. Illustratively, the functional material is present in an amount of 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt% or a range of any two of the foregoing values.

In some embodiments, the separator is disposed after the secondary battery is subjected to the formation process, and the internal resistance of the secondary battery is 8 Ω to 16 Ω, and illustratively, the internal resistance of the secondary battery is 8 Ω, 9 Ω, 10 Ω, 12 Ω, 13 Ω, 14 Ω, 15 Ω, 16 Ω, or a range of any two of the above values.

In some embodiments, the adhesion between the separator and the pole piece is 6N to 15N. Illustratively, the bond between the separator and the pole piece is in the range of 6N, 8N, 10N, 12N, 13N, 15N, or any two of the values recited above.

Others

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the thickness of the positive electrode active material layer is not particularly limited as long as the object of the present application can be achieved, for example, the positive electrode active material layer has a thickness of 30 μm to 120 μm. The positive electrode active material in the positive electrode active material layer may be one or more selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and compounds obtained by adding other transition metals or non-transition metals to the above compounds. The positive electrode current collector may be a metal foil or a porous metal plate, for example, a foil or a porous plate of a metal such as aluminum, copper, nickel, titanium, or iron, or an alloy thereof, such as an Al (aluminum) foil. The thickness of the positive electrode current collector is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the cathode current collector is 5 μm to 12 μm. The cathode sheet may be prepared according to conventional methods in the art.

The anode tab includes an anode current collector and an anode active material layer provided on the anode current collector, and the thickness of the anode active material layer is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the anode active material layer is 30 μm to 120 μm. The negative electrode active material layer contains a negative electrode active material. In some embodiments, the anode active material may include at least one of a carbon material or a silicon-based material. In some embodiments, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, or soft carbon. In some embodiments, the silicon-based material includes, but is not limited to, at least one of silicon, a silicon oxygen composite, or a silicon carbon composite. The negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, and may include, for example, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, or a composite current collector (for example, a composite current collector in which a metal layer is provided on the surface of a polymer layer), or the like. The thickness of the negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the negative electrode current collector is 5 μm to 12 μm. The anode active layer may further include a binder and a thickener, and the kind of the binder and the thickener is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The anode active layer may further include a conductive agent, and the kind of the conductive agent is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon Nanotubes (CNTs), carbon fibers, ketjen black, graphene, metallic materials, or conductive polymers. The mass ratio of the anode active material, the conductive agent, the binder and the thickener in the anode active layer is not particularly limited in this application, and one skilled in the art may select according to actual needs as long as the object of this application can be achieved. Optionally, the negative electrode tab may further comprise a conductive layer located between the negative electrode current collector and the negative electrode active layer. The composition of the conductive layer is not particularly limited in this application, and may be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in this application, and may be at least one of the conductive agent and the binder in the anode active layer described above, for example. The negative electrode sheet may be prepared according to conventional methods in the art.

In some embodiments, the surface of the pole piece is provided with an embossed area, the pole piece comprises a first area and a second area along the length direction of the pole piece, the first area is a single-sided coating area, the second area is a double-sided coating area, the coating surface of the first area is provided with a first embossing, and the first embossing is formed by sequentially applying 0.3 Mpa-0.4 Mpa force to the pole piece through a plurality of spherical protrusions with the particle size of 1.0 mm-5 mm. The coating surfaces on two sides of the second area are respectively provided with a second embossing, and the second embossing is formed by sequentially applying 0.3 Mpa-0.4M acting force to the polar plate through a plurality of spherical bulges with the particle size of 5.0 mm-10 mm.

Referring to fig. 3, taking the positive electrode sheet 102 as an example, an embossed area is disposed on the surface of the positive electrode sheet 102, the positive electrode sheet 102 includes a first area 1021 and a second area 1022 along the length direction W of the positive electrode sheet, the first area 1021 is coated on one side, the second area 1022 is coated on two sides, a first embossing is disposed on the coated surface of the first area 1021, and a second embossing is disposed on the coated surfaces on two sides of the second area 1022.

In some embodiments, the first embossment has an embossment depth-to-diameter ratio in the range of 1 (0.7-1), the second embossment has an embossment depth-to-diameter ratio in the range of 1 (0.5-0.8), and the first and second regions have an area ratio of 1 (6-12). The embossing area is arranged on the surface of the negative electrode plate, and the embossing area can be set by referring to the embossing area of the positive electrode plate, and the details are omitted.

Electronic equipment

The electronic equipment comprises any secondary battery. The electronic device of the application includes, but is not limited to, a mobile phone, a notebook computer, a tablet computer, a game console, an unmanned aerial vehicle, an electric automobile, an electric bicycle, an electric tool, a Bluetooth headset and the like.

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples.

Example 1-1

Preparation of lithium ion battery

(1) Preparation of lithium ion battery isolation film

And (3) selecting a base film with a closed-pore temperature of 135 ℃, coating slurry containing polymer particles on the surfaces of both sides of the base film by adopting a micro-gravure coating process, and drying to prepare a polymer particle layer, thereby obtaining the isolation film.

Preparation of polymer particles: adding a certain amount of deionized water into a constant temperature water bath at 80 ℃, adding 65 parts of styrene, 5 parts of isooctyl methacrylate, 5 parts of methyl methacrylate and 75 parts of butadiene, adding a certain amount of emulsifier, namely 3 parts of sodium dodecyl sulfate and 1 part of octyl phenol polyoxyethylene ether, firstly crosslinking and emulsifying the hard component monomers for 1h, then adding shell monomers, namely 5 parts of isooctyl acrylate, 2 parts of ethylene glycol dimethacrylate, 5 parts of isobutyl methacrylate, 5 parts of methacrylic acid and 3 parts of acrylonitrile, adding an initiator at the same time, starting a reaction tank at the same time, slowly stirring for 300r/min, cooling to 60 ℃ after the addition is finished, and keeping the temperature for continuous reaction for 1.5h. After the reaction is completed, cooling the mixture to room temperature, regulating Ph to be neutral by ammonia water, filtering and discharging, and dispersing the prepared microspheres into water according to a certain solid content to prepare emulsion.

Preparation of the coating slurry: the emulsion prepared by the method is prepared by adding 87wt% of microspheres, 3wt% of styrene-butadiene rubber, 1wt% of carboxymethyl cellulose and 9 wt% of dimethyl siloxane into a stirring tank, and stirring and dispersing uniformly.

Examples 1-1 to 1-20 and comparative examples 1 to 4 differ from example 1-1 in that: the examples 1-1 to 1-20 were each adjusted in the kind and proportion of monomers used in the preparation of polymer particles, and the other parts were the same as in example 1-1, and are shown in Table 1.

Examples 2-1 to 2-17 differ in that: the examples 2-1 to 2-17 each adjust various parameters of the polymer particles, including the size and content of the polymer particles, the ratio of the first polymer to the second polymer, the types and content of the functional substances, and the other parts are the same as those of the example 1-1, and see table 2 in detail.

(2) Preparation of positive electrode plate

Lithium cobalt oxide LiCoO as cathode active material ₂ Fully stirring conductive carbon black Super-P and a binder PVDF in an N-methylpyrrolidone NMP solvent system according to a weight ratio of 97.6:1.3:1.1 by a vacuum stirrer to obtain cathode slurry; coating the cathode slurry on two surfaces of a 9 mu m Al foil substrate, wherein the coating weight is280mg, drying, cold pressing, slitting and cutting to obtain the positive pole piece, wherein the thickness of the positive pole piece after cold pressing is 95 mu m.

Example 3-1 to example 3-25 the difference between example 1-1 is that: the positive electrode sheets were subjected to the embossing treatments defined by different parameters in examples 3-1 to 3-25, respectively, and the other parts were the same as in example 1-1, and the details are shown in table 3.

(3) Preparation of negative electrode plate

Uniformly mixing anode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR) and thickener methyl cellulose sodium (CMC) in deionized water solvent according to a mass ratio of 95:2:2:1, coating the mixture on one side surface of a Cu foil with the thickness of 9 mu m, drying the mixture, repeating the steps on the other side surface of the Cu foil to obtain an anode plate with the anode active layer coated on both sides, and carrying out cold pressing and cutting to obtain a cathode plate.

(4) Preparation of electrolyte

Uniformly mixing Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) according to the mass ratio of 1:1:1 to obtain the organic solvent. LiPF is put into ₆ Dissolving in the organic solvent, adding vinylene carbonate (additive), and mixing to obtain electrolyte. Wherein based on the total mass of the electrolyte, the LiPF ₆ The mass percentage of the ethylene carbonate is 12.5 percent, and the mass percentage of the vinylene carbonate is 3 percent.

(5) Preparation of lithium ion batteries

And sequentially stacking the cathode pole piece, the isolating film and the anode pole piece, enabling the isolating film to isolate the cathode pole piece and the anode pole piece, winding to form a bare cell, placing the bare cell into an aluminum plastic film of a shell to be sealed, and performing high-temperature baking, electrolyte injection, vacuum packaging, standing, formation, shaping, capacity testing and other procedures to obtain the lithium ion battery.

Chemical process parameters: the temperature is 80-90 ℃ and the pressure is 0.8 Mp-1.2 Mpa.

Testing of lithium ion batteries

(1) Circulation test (remark: 1C current 5000 mA)

(a) Cycle test at 10 ℃ 1C:

1) The test temperature was 10 ℃; 2) Standing for 60min; 3) Charging to 4.5V at 1C cross current, and charging to 0.05C at constant voltage; 4) Standing for 5min; 5) Discharging to 3V at 0.5C; 6) Standing for 5min; 7) Step 3 to step 6 are cycled 500 times.

(b) Cycling test at 25 ℃ 3C:

1) The test temperature was 25 ℃; 2) Standing for 30min; 3) Charging to 4.3V at 3.0C constant current; 4) Charging to 4.35V at constant current of 2.5C; 5) Charging to 4.5V at constant current of 2.0C, and charging to 0.05C at constant voltage; 6) Standing for 5min; 7) Discharging to 3V at 0.5C; 8) Standing for 5min 9) and circulating the steps 3 to 9 for 1000 times.

(c) Cyclic test at 45 ℃ 3C:

1) The test temperature was 45 ℃; 2) Standing for 30min; 3) 3.0C constant current charging to 4.3V; 4) Constant current charging of 2.5C to 4.35V; 5) Constant-current charging to 4.5V at 2.0C and constant-voltage charging to 0.05C; 6) Standing for 5min; 7) 0.5C discharges to 3V; 8) Standing for 5min 9) and circulating 500 times from the 3 rd step to the 9 th step

(d) High temperature storage test at 80 ℃):

the cells were charged fully and stored in a high temperature oven at 80 ℃ for 42h.

Full filling step:

1) The test temperature was 25 ℃; 2) Standing for 5min; 3) Constant-current charging of 6A to 4.5V and constant-voltage charging to 0.02C; 4) Standing for 5min; 5) 0.2C is discharged to 3V; 6) Standing for 5min; 7) Constant-current charging of 6A to 4.5V and constant-voltage charging to 0.02C; and after full charge, testing the thickness, internal resistance and voltage of the battery cell. After storing at 80 ℃ for 42 hours, the thickness, internal resistance and voltage were measured again. And discharging and fully charging the battery cells after storage.

1) The test temperature was 25 ℃; 2) Standing for 5min; 3) 0.2C is discharged to 3V; 4) Standing for 5min; 5) Constant-current charging of 6A to 4.5V and constant-voltage charging to 0.02C; 6) Standing for 5min; 7) 0.2C is discharged to 3V; 8) Standing for 5min.

(2) Adhesive force test:

and respectively selecting 100mm-300mm isolating films, anode and cathode samples, and punching the sampled samples into 54.2 x 72.5mm samples by using a paper package, a cutting die and a punching machine. The punched diaphragm and the anode are orderly stacked, the diaphragm faces upwards, the size of each pad 130mm is 130mm, the teflon is arranged on the upper pad and the lower pad, the stacked sample is placed in the middle of the cardboard, and a 150mm 160mm clamp is covered on the cardboard. The laminated sample is put into a flat press to adjust the pressure and the air pressure, the pressure=400+ -10 KG.T=85 ℃ and the time is set to 80S. The hot pressed samples were die cut into strips of 72.5mm x 15mm using a knife die and punch. Separating the isolating film from the pole piece, connecting the diaphragm sample (paper strip is placed between the diaphragm and the pole piece) by using A4 paper with the width of 15mm, and adhering crepe adhesive (which cannot be adhered to a steel plate) on two sides of the connecting part to finish the sample preparation. Separating the isolating film from the pole piece, connecting the diaphragm sample (paper strip is placed between the diaphragm and the pole piece) by using A4 paper with the width of 15mm, and adhering crepe adhesive (which cannot be adhered to a steel plate) on two sides of the connecting part to finish the sample preparation. And placing the sample to be tested between the clamps, fixing the tail end of the steel plate on the lower clamping head, fixing the A4 paper on the upper clamping head, and respectively clamping the upper and lower clamping heads by the clamps. Clicking an operation interface of stretching of a computer desktop, clearing force, displacement and the like, clicking 'start', prestretching by 5mm, clearing force, displacement and the like again after prestretching, starting testing, and after testing, deriving and storing complete data.

TABLE 1

It can be seen from the data in table 1 that the lithium ion battery meets the requirements of proper types among the monomers, is more beneficial to improving the cycle performance of the lithium ion battery, and is more beneficial to ensuring that the internal resistance and the cohesive force of the lithium ion battery after formation are in ideal ranges. When the mass ratio of each monomer is proper, the cycle performance of the lithium ion battery can be improved, and the internal resistance and the cohesive force of the lithium ion battery after formation are ensured to be in proper ranges.

TABLE 2

By combining table 1 and examples 1-1 to 1-18, it can be seen that when all parameters of the polymer particles are in the appropriate ranges, the cycle performance of the lithium ion battery can be improved, the high-temperature storage performance of the lithium ion battery can be further improved, and the expansion rate of the lithium ion battery at a high temperature is in a controllable range. In particular examples 1 to 14, examples 1 to 14 had a capacity retention rate of up to 90% at 45℃for 500 cycles at 3C, a residual capacity retention rate of up to 90% at 80℃for 42 hours, and a small swolling (expansion rate) at high temperatures of not more than 8%. Compared with examples 1-1 to 1-5, it can be seen that if the ratio of the first polymer is too high based on the mass of the polymer particles, the improvement of the high-temperature performance of the lithium ion battery is not facilitated, the internal resistance after formation is too high, the binding force is too high, the dynamic performance of the battery is poor, and the cycle skip easily occurs in the later stage of the cycle. If the second polymer has too high a duty ratio, the adhesive force between the isolating film and the pole piece is weaker, which is unfavorable for improving the performance of the battery. Examples 1-7 to 1-13 are compared with examples 1-2, and it can be seen that the polymer particles have unsuitable particle diameters and are also disadvantageous for improving the high temperature performance of lithium ion batteries. Examples 1-14 to 1-18 compared with examples 1-2, it can be seen that the polymer particles have an unsuitable ratio based on the mass of the polymer particle layer, which is disadvantageous for improving the high temperature storage performance of the lithium ion battery, and the expansion rate thereof at high temperature is large and uncontrollable.

TABLE 3 Table 3

It can be seen from table 3 that the depth-to-diameter ratio and the area ratio of the first embossed region and the second embossed region are in proper ranges, so that the retention amount of electrolyte in the corner region of the lithium ion battery can be improved, and the cycle performance of the lithium ion battery can be improved.

The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.

Claims

1. A separator characterized in that the separator comprises a base film and a polymer particle layer arranged on at least one side surface of the base film;

the polymer particle layer comprises polymer particles, and the shell of the polymer particles comprises a first polymer generated by polymerization of a monomer I, a monomer II and a monomer III;

the monomer I comprises methacrylate monomers or styrene, and the glass transition temperature of the monomer I is 8-80 ℃;

the monomer II comprises at least one of acrylic ester monomers, acrylic alcohol ester monomers and acrylic acid monomers;

the monomer III comprises acrylonitrile.

2. The separator of claim 1, wherein at least one of the following conditions is satisfied:

(1) The monomer I is selected from butyl methacrylate and/or isobutyl methacrylate, and the glass transition temperature is 20-53 ℃;

(2) The monomer II is at least one selected from isobutyl acrylate, isooctyl acrylate, ethylene glycol dimethacrylate, methacrylic acid or acrylic acid;

(3) The first polymer has a number average molecular weight of 15 to 30 tens of thousands.

3. The isolating membrane according to claim 1, wherein the mass ratio of the monomer I, the monomer II and the monomer III is (0.5-1): 2-2.5): 0.3-0.6.

4. The barrier film of claim 1, wherein the inner core of the polymer particles comprises a second polymer formed by polymerization of monomer IV and monomer V;

the monomer IV comprises a styrene monomer and/or an acrylic monomer, and the glass transition temperature of the monomer IV is 105-120 ℃;

the monomer V comprises butadiene;

the mass ratio of the monomer IV to the monomer V is 1 (1-1.2).

5. The separator as claimed in claim 1, wherein,

the mass percent of the polymer particles is 80wt% to 90wt% based on the mass of the polymer particle layer;

the average particle diameter of the polymer particles is 0.5-1.2 nm.

6. The separator of claim 4, wherein the mass percent of the first polymer is 20wt% to 40wt% and the mass percent of the second polymer is 60wt% to 80wt%, based on the mass of the polymer particles.

7. A secondary battery, characterized in that the secondary battery comprises a winding type cell;

the wound cell comprising a pole piece and the separator of any one of claims 1 to 6;

the surface of the pole piece is provided with an embossing area, and at least part of the embossing area is arranged in the corner area of the winding type battery cell.

8. The secondary battery according to claim 7, wherein the pole piece includes a first region and a second region along a length direction thereof, the first region being a single-sided coating region, the second region being a double-sided coating region;

the coating surface of the first area is provided with a first embossing and the coating surface of the second area is provided with a second embossing.

9. The secondary battery according to claim 8, wherein at least one of the following conditions is satisfied:

(1) The embossing depth-diameter ratio range of the first embossing is 1 (0.7-1);

(2) The embossing depth-diameter ratio range of the second embossing is 1 (0.5-0.8);

(3) The area ratio of the first area to the second area is 1 (6-12).

10. An electronic device characterized in that the electronic device comprises the secondary battery according to any one of claims 7 to 9.