CN112909431B - Lithium ion battery composite diaphragm, preparation method thereof and lithium ion battery - Google Patents
Lithium ion battery composite diaphragm, preparation method thereof and lithium ion battery Download PDFInfo
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- CN112909431B CN112909431B CN202110094106.2A CN202110094106A CN112909431B CN 112909431 B CN112909431 B CN 112909431B CN 202110094106 A CN202110094106 A CN 202110094106A CN 112909431 B CN112909431 B CN 112909431B
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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Abstract
The invention provides a lithium ion battery composite diaphragm, a preparation method thereof and a lithium ion battery. The invention provides a lithium ion battery composite diaphragm, which comprises: a polymeric porous separator layer and a vinylidene fluoride-containing homopolymer and/or copolymer film layer on at least one side of the polymeric porous separator layer; the film layer containing vinylidene fluoride homopolymer and/or copolymer is prepared by a melt extrusion method by using a composition containing the vinylidene fluoride homopolymer and/or copolymer, wherein the composition comprises the following components in percentage by weight: 65-98% of vinylidene fluoride homopolymer and/or copolymer, 0-25% of ceramic particles and 0-10% of modification auxiliary agent; the lithium ion battery provided by the invention comprises the lithium ion battery composite diaphragm.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery composite diaphragm, a preparation method thereof and a lithium ion battery containing the composite diaphragm.
Background
With the development of new energy technology, the lithium ion battery industry used in the fields of power automobiles, 3C electronic products and the like is rapidly developed. The lithium ion battery is mainly composed of a positive electrode, a negative electrode, electrolyte, a diaphragm and the like, and has the advantages of high energy density, high working voltage and long cycle life. The lithium ion battery diaphragm is used as one of key components of the lithium ion battery, is mainly used for isolating the positive electrode and the negative electrode, provides a lithium ion crossing channel between the positive electrode and the negative electrode, and has the electrolyte absorption and retention capacity so as to realize the normal cycle charge and discharge work of the lithium ion battery. The lithium ion battery diaphragm does not directly participate in the electrochemical reaction, but directly influences the capacity, charge-discharge current density, cycle, safety performance and other characteristics of the lithium ion battery.
In actual use, on one hand, the battery can cause the diaphragm to shrink and deform in a high-power charging and discharging process and under the external influence of extrusion, puncture and the like, so that the short circuit of the positive electrode and the negative electrode inside the battery is caused, thermal runaway is formed, and spontaneous combustion or explosion occurs; on the other hand, the bonding force between the diaphragm product and the battery pole piece is weak, so that the diaphragm and the pole piece are easy to separate in the charging and discharging process of the battery, and the performances of the battery such as the cycle life and the like are reduced; on the other hand, the traditional diaphragm has poor wettability and liquid retention to electrolyte, so that the safety of the battery and the consistency of the battery core are reduced.
The existing solutions are mainly to coat one or more layers of functional coatings, such as polyvinylidene fluoride (PVDF) coatings, ceramic coatings, aramid coatings, etc., on the surface of the diaphragm. For example, at present, the technicians adopt the following schemes: 1. the preparation method comprises the steps of preparing the low-solid-content water-based PVDF slurry, coating and drying the slurry to form a coating on the surface of a base film, so that the adhesion between a diaphragm and a pole piece is improved, the hardness of the pole piece and the effective utilization space of a battery are improved, and the ventilation loss caused by the thick coating is reduced. 2. One side of the base film is coated with the aramid fiber coating and the other layer of the base film is coated with the PVDF coating, and the diaphragm has good thermal property and mechanical property of the aramid fiber coating, and meanwhile has good wettability and liquid retention of the PVDF coating on electrolyte, so that the battery and the pole piece are effectively bonded. 3. The aluminum oxide ceramic coating slurry is uniformly coated on the surface of the diaphragm, so that the safety of the battery is improved, and the cycle life of the battery is prolonged. 4. PVDF-HFP and ceramic are mixed according to a certain proportion to prepare slurry to be coated on a base membrane, and the composite modified membrane with good permeability and low permeability is obtained. 5. An environment-friendly breathable safe battery diaphragm is researched, wherein a water-based ceramic layer is coated on the surface layer of the diaphragm, and a water-based PVDF (polyvinylidene fluoride) point adhesive layer is further coated on the outer surface of the water-based ceramic layer.
In summary, in any of the above technical solutions, the existing preparation process of the coating diaphragm at least includes the steps of slurry preparation, coating drying and the like, and the common problems of complex slurry formula, poor uniformity and stability, complex coating process, harsh conditions and the like exist, so that the production efficiency of the product is reduced, and the yield is reduced.
In addition, when organic solvents such as acetone and the like are adopted to prepare coating slurry, after the surface of the diaphragm is coated, the organic slurry has good compatibility with the diaphragm, and the slurry can permeate into micropores of the diaphragm, so that the diaphragm is easy to block the pores, the air permeability loss is large, and the battery performance is influenced; organic solvents and other organic additives are used in the slurry formula, and are usually toxic, inflammable, explosive and volatile, so unsafe factors are brought to the production process, and special and complicated preparation measures are required.
When the aqueous mixture is used as coating slurry, PVDF and the like are suspended in the slurry in a granular form, and the granular PVDF is distributed on the surface of a base film after coating and drying, so that the contact area between the PVDF and a pole piece is small, and the generated bonding performance is poor.
Disclosure of Invention
In view of the above, in order to improve the heat resistance of the separator product and the adhesive property with the electrode plate, and effectively improve the simplicity of the preparation process of the functional coating, and the uniformity of the functional coating is stable, the invention provides a lithium ion battery composite separator, a preparation method thereof, and a lithium ion battery containing the composite separator, so as to solve the existing technical problems.
In order to achieve the purpose, the invention provides a lithium ion battery composite diaphragm, a preparation method thereof and a lithium ion battery containing the composite diaphragm. In one aspect, the present invention provides a lithium ion battery composite separator, including: a polymeric porous separator layer and a vinylidene fluoride-containing homopolymer and/or copolymer film layer on at least one side of the polymeric porous separator layer; the film layer containing vinylidene fluoride homopolymer and/or copolymer is prepared by melt extrusion method by using a composition containing the vinylidene fluoride homopolymer and/or copolymer, wherein the composition comprises the following components in percentage by weight: 65-98% of vinylidene fluoride homopolymer and/or copolymer, 0-25% of ceramic particles and 0-10% of modification auxiliary agent.
According to an embodiment of the invention, wherein the polymer porous separator layer comprises one of: polyethylene single-layer diaphragm, polypropylene/polyethylene/polypropylene multi-layer diaphragm, polyethylene/polypropylene/polyethylene multi-layer diaphragm, polytetrafluoroethylene diaphragm, polyamide diaphragm, polyimide diaphragm, cellulose diaphragm, polyethylene terephthalate diaphragm.
According to an embodiment of the invention, wherein the melting point T of the vinylidene fluoride homopolymer and/or copolymer m The melt flow rate is 0.6-6.0 g/10min at 125-185 ℃.
According to an embodiment of the invention, wherein the vinylidene fluoride homo-and/or copolymer comprises at least one of: polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-pentafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer.
According to an embodiment of the invention, wherein the ceramic particles comprise at least one of: alumina, silica, titania, zirconia, ceria, lithium aluminum titanium phosphate; the average particle diameter of the ceramic particles is 10 to 600 nm.
According to an embodiment of the invention, wherein the modification aid comprises a tackifying resin and a processing aid, wherein the tackifying resin comprises at least one of: polyacrylic acid, polymethacrylic acid, polymethylmethacrylate, polybutylmethacrylate, polyethylacrylate, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer; the processing aid comprises an antioxidant and a dispersant.
On the other hand, the invention provides a preparation method of a lithium ion battery composite diaphragm, so as to obtain the lithium ion battery composite diaphragm, and the method comprises the following steps: preparing a vinylidene fluoride homopolymer and/or copolymer-containing film from a blend containing 65-98 wt% of vinylidene fluoride homopolymer and/or copolymer, 0-25 wt% of ceramic particles and 0-10 wt% of modification aid by a melt extrusion method; and sequentially stacking the vinylidene fluoride homopolymer and/or copolymer-containing film on at least one side of the polymer porous diaphragm and carrying out hot pressing to prepare the lithium ion battery composite diaphragm.
According to the embodiment of the invention, the thickness of the film containing the vinylidene fluoride homopolymer and/or copolymer is 4-25 μm.
According to an embodiment of the invention, wherein the melt extrusion process comprises one of: a single-layer film blowing method, a multi-layer film blowing method, a single-layer casting method, a multi-layer casting method, and a casting stretching method.
In another aspect, the present invention further provides a lithium ion battery, including: the lithium ion battery comprises a positive electrode, a negative electrode, electrolyte, a composite diaphragm and the like, wherein the composite diaphragm is the lithium ion battery composite diaphragm prepared by the preparation method.
According to the embodiment of the invention, the functional layer containing the vinylidene fluoride homopolymer and/or copolymer is independently prepared by adopting a melt extrusion method through the lithium ion battery composite diaphragm and the preparation method thereof, the preparation process flow is simple, and the product performance is uniform and stable; the heat resistance and the pole piece bonding performance of the polymer porous diaphragm are obviously improved, and the safety of the lithium ion battery prepared by the composite diaphragm is also greatly improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 schematically illustrates a flow chart of a method for preparing a lithium ion battery composite separator according to an embodiment of the invention;
FIG. 2 schematically shows a flow chart of a method for preparing a vinylidene fluoride-containing homopolymer or/and copolymer film according to an embodiment of the present invention;
fig. 3 schematically shows a process diagram for preparing a lithium ion battery composite separator by stacking a functional coating on one side of a polymer porous separator according to an embodiment of the present invention;
fig. 4 schematically shows a process diagram for preparing a lithium ion battery composite separator by stacking functional coatings on both sides of a polymer porous separator according to an embodiment of the present invention.
Detailed Description
In the related technical field, when the lithium ion battery diaphragm is used for preparing a battery core, a polymer porous diaphragm is generally adopted for lamination or winding forming. If the functional coating can be independently prepared into a roll film, and the steps of multi-step and multi-parameter control coating, drying and the like are converted into a roll-to-roll hot press forming process, the forming efficiency and the uniformity and stability of product performance can be obviously improved.
Based on the above conception, the invention provides a lithium ion battery composite diaphragm, a preparation method thereof and a lithium ion battery containing the composite diaphragm, wherein the composite diaphragm can maintain the performance of the lithium ion battery, can improve the pole piece cohesiveness and the shape stability based on high heat resistance, has feasibility of efficient, stable and large-scale forming preparation, and has very important practical significance for promoting the development of high-performance and high-safety lithium ion batteries.
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. Other embodiments, which can be derived by one of ordinary skill in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The endpoints of the ranges and any values disclosed in the present application are not limited to the precise range or value and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual values, and between the individual values may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a lithium ion battery composite diaphragm, a preparation method thereof and a lithium ion battery containing the composite diaphragm. Wherein, this lithium ion battery composite membrane includes: a polymeric porous separator layer and a vinylidene fluoride-containing homopolymer and/or copolymer film layer on at least one side of the polymeric porous separator layer; wherein the film layer containing the vinylidene fluoride homopolymer and/or copolymer is prepared by a melt extrusion method by using a composition containing the vinylidene fluoride homopolymer and/or copolymer, and the composition comprises the following components in percentage by weight: 65-98% of vinylidene fluoride homopolymer and/or copolymer, 0-25% of ceramic particles and 0-10% of modification auxiliary agent.
According to embodiments of the present invention, the polymeric porous separator layer includes, but is not limited to: polyethylene single-layer diaphragm, polypropylene/polyethylene/polypropylene multi-layer diaphragm, polyethylene/polypropylene/polyethylene multi-layer diaphragm, polytetrafluoroethylene diaphragm, polyamide diaphragm, polyimide diaphragm, cellulose diaphragm, polyethylene terephthalate diaphragm.
According to embodiments of the present invention, the vinylidene fluoride-containing homopolymer and/or copolymer film layer on at least one side of the polymeric porous separator layer may comprise: laminating and hot-pressing a vinylidene fluoride-containing homopolymer and/or copolymer film layer on one side of a polymer porous separator layer; alternatively, a vinylidene fluoride-containing homopolymer and/or copolymer film layer is laminated and heat pressed on both sides of a polymeric porous separator layer.
According to an embodiment of the invention, the vinylidene fluoride homo-and/or copolymer comprises at least one of: polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-pentafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer.
According to the embodiment of the present invention, the vinylidene fluoride-hexafluoropropylene copolymer is not limited to a certain vinylidene fluoride-hexafluoropropylene copolymer, and may be a blend of different vinylidene fluoride-hexafluoropropylene copolymers, or polyvinylidene fluoride may be added to the vinylidene fluoride-hexafluoropropylene copolymer, and the polyvinylidene fluoride can improve the melt processability of the vinylidene fluoride-hexafluoropropylene copolymer, but can reduce the adhesiveness of the film. Therefore, it is preferable that the mass of the polyvinylidene fluoride added is not more than 25% of the total mass of the vinylidene fluoride-hexafluoropropylene copolymer.
According to an embodiment of the invention, wherein the melting point T of the vinylidene fluoride homopolymer and/or copolymer m The melt flow rate is between 125 and 185 ℃ and between 0.6 and 6.0g/10 min.
According to the embodiment of the present invention, the lower the melting point of the vinylidene fluoride homopolymer and/or copolymer is, the better the adhesion when used between the pole piece and the separator is, and the higher the melting point is, the better the heat resistance of the vinylidene fluoride-containing homopolymer and/or copolymer film is. Thus, the melting point T of vinylidene fluoride homopolymers and/or copolymers m Preferably 140 to 175 ℃.
According to the examples of the present invention, the melt flow rate of the vinylidene fluoride homopolymer and/or copolymer is closely related to the melt viscosity of the copolymer and the melt strength at the time of processing, and the bubble stability at the time of processing becomes higher as the melt flow rate becomes smaller, but the screw torque increases when the melt flow rate becomes too small. Therefore, the melt flow rate of the vinylidene fluoride homopolymer and/or copolymer at the temperature of 230 ℃ and under the load of 2.16kg is 0.6-6.0 g/10min, preferably 0.6-4.0 g/10 min.
According to embodiments of the invention, the ceramic particles may comprise one or more of: alumina, silica, titania, zirconia, ceria, lithium titanium aluminum phosphate; the average particle diameter of the ceramic particles is 10 to 600 nm.
According to the embodiment of the invention, the heat resistance and the dimensional stability of the composite diaphragm can be improved by adding the ceramic particles; the electrical properties of the composite separator may also be improved. However, when the content of the ceramic particles is too large, melt processability during melt extrusion is remarkably lowered, and defects such as bubble breakage occur, so that film formation is difficult.
According to embodiments of the present invention, the modification aids may include tackifying resins and processing aids. The adhesion of the film containing vinylidene fluoride homopolymer and/or copolymer can be further improved by adding the tackifying resin, and the crystallinity and the grain size of the film containing vinylidene fluoride homopolymer and/or copolymer can be reduced during film forming; the addition of the processing aid can prevent the problems of thermal degradation, agglomeration of ceramic particles and the like of vinylidene fluoride homopolymer and/or copolymer resin materials in the vinylidene fluoride homopolymer and/or copolymer-containing composition in the melt extrusion process.
According to an embodiment of the invention, the tackifying resin comprises one or several of the following: polyacrylic acid, polymethacrylic acid, polymethylmethacrylate, polybutylmethacrylate, polyethylacrylate, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer.
According to embodiments of the present invention, processing aids include, but are not limited to, antioxidants, dispersants. Wherein, the antioxidant comprises one or more of the following components: hindered amine antioxidants, phenol antioxidants, phosphite antioxidants, and the like; the dispersant comprises one or more of the following components: silane coupling agent, titanate coupling agent, aluminate coupling agent, fatty acid/ester surfactant and the like. In addition, in order to prevent the agglomeration of the ceramic particles, surface modification or coating treatment of the ceramic particles may be employed.
The invention also provides a preparation method of the lithium ion battery composite diaphragm, so as to obtain the lithium ion battery composite diaphragm. Fig. 1 schematically shows a flow chart of a method for preparing a lithium ion battery composite separator according to an embodiment of the present invention.
As shown in fig. 1, the preparation method includes operations S101 to S102.
In operation S101, a blend containing 65 to 98wt% of a vinylidene fluoride homopolymer and/or copolymer, 0 to 25 wt% of ceramic particles, and 0 to 10wt% of a modification aid is melt-extruded to prepare a film containing the vinylidene fluoride homopolymer and/or copolymer.
In operation S102, a vinylidene fluoride-containing homopolymer and/or copolymer film is sequentially stacked on at least one side of a polymer porous separator and hot-pressed, to prepare a lithium ion battery composite separator.
In the embodiment of the invention, fig. 2 schematically shows a flow chart of a preparation method of a vinylidene fluoride-containing homopolymer or/and copolymer film according to the embodiment of the invention.
As shown in fig. 2, the method of preparing the film containing the vinylidene fluoride homopolymer and/or copolymer in step S101 further includes operations S101-1 to S101-3.
In operation S101-1, 65-98 wt% of vinylidene fluoride homopolymer and/or copolymer, 0-25 wt% of ceramic particles and 0-10 wt% of modification auxiliary agent are weighed and uniformly mixed to obtain the blend containing the vinylidene fluoride homopolymer and/or copolymer.
According to the embodiment of the invention, the raw materials are put into the high-speed mixer to be uniformly mixed, the high-speed mixing of the high-speed mixer can ensure that various raw materials are fully mixed before entering the hopper of the extruder, and the dispersion of the ceramic particles and the processing aid is facilitated by the increase of the rotating speed and the mixing time.
According to the embodiment of the invention, the rotating speed of the high-speed mixer can be 2000-5000 r/min, and the mixing time can be 0.5-2.5 h.
Melting Point T of vinylidene fluoride homopolymers and/or copolymers according to embodiments of the present invention m Is 125 to 185 ℃, preferably 140 to 175 ℃; the melt flow rate is 0.6-6.0 g/10min, preferably 0.6-4.0 g/10min at the temperature of 230 ℃ and under the condition of the load of 2.16 kg.
In operation S101-2, the blend containing the vinylidene fluoride homopolymer and/or copolymer is melt-blended and pelletized to obtain pellets containing the vinylidene fluoride-hexafluoropropylene copolymer.
According to the embodiment of the present invention, the melt blending granulation machine is not limited, and a mixing roll, a twin-screw extruder, and various derivative extruders based on the above-mentioned machines may be used, and more preferably, a twin-screw extruder having a vent system may be selected.
According to the embodiment of the invention, after the blend is subjected to melt blending and granulation to obtain the granules, the granules are subjected to drying pretreatment to prevent the phenomena of air bubbles, degradation and the like in the film processing process, and the water content of the liquid crystal polymer after the drying treatment is not higher than 1000ppm, preferably not higher than 500 ppm. The present invention is not particularly limited with respect to the dried form. Specifically, for example, pellets containing a vinylidene fluoride-hexafluoropropylene copolymer are placed in a blast or vacuum drying oven and dried for 1 hour or more or below the glass transition temperature.
In operation S101-3, the pellets are used to prepare a vinylidene fluoride-containing homopolymer and/or copolymer film having a predetermined thickness by a melt extrusion method.
According to an embodiment of the present invention, the above pellets are fed from a hopper into an extruder, and a thin film of a vinylidene fluoride-containing homopolymer and/or copolymer is produced by a film blowing apparatus or a casting apparatus.
According to the embodiment of the invention, the thickness of the prepared vinylidene fluoride-containing homopolymer and/or copolymer film with the preset thickness is 4-25 μm, and the film is difficult to directly prepare by a melt extrusion method due to the excessively small thickness, the ionic conductivity of the film is reduced due to the excessively large thickness, and the electrochemical performance is difficult to meet the requirements of a lithium ion battery. Therefore, the film thickness is preferably 4 to 20 μm.
According to embodiments of the present invention, melt extrusion processes include, but are not limited to: a single-layer film blowing method, a multi-layer film blowing method, a single-layer casting method, a multi-layer casting method, and a casting stretching method. The preferable film preparation method can be a single layer film blowing method, a multilayer film blowing method and a multilayer casting method.
The extruder used for preparing the vinylidene fluoride-containing homopolymer and/or copolymer film according to the embodiments of the present invention is also not particularly limited, and may be a single screw extruder, a twin screw extruder, and various derived extruders based on the above.
In accordance with embodiments of the present invention, for example, in the case of a conventional single screw extruder, the process parameter ranges required for preparing a vinylidene fluoride-containing homopolymer and/or copolymer film of a predetermined thickness from the pellets using a melt extrusion process may include:
the temperature of the charging section is T m +/-20 deg.C and compression temp. of T m +10℃～T m +60 ℃ and a homogenization section temperature T m +20℃～T m +80 ℃; die temperature of T m +15℃～T m +70 ℃; more preferably the temperature of the feeding section is T m +/-10 deg.C and compression temp at T m +15℃～T m +50 ℃ and a homogenization section temperature T m +25℃～T m +70 ℃; die temperature of T m +20℃～T m +65℃。
According to the embodiment of the present invention, since the temperature of the feeding section is lower than T m At-20 ℃ the single screw extruder will not provide sufficient forward driving force to move the material into the compression section if the temperature in the feed section is above T m +20 ℃ the vinylidene fluoride homopolymer or/and copolymer particles melt in the feeding section due to the excessive temperature and cannot enter the compression section. If the temperature of the compression section is lower than T m +10 ℃ the material cannot be completely plasticized in the compression section, if the temperature is above T m +60 c, it is then very easy for the melt to crack, resulting in unstable front pressure.
According to an embodiment of the present invention, the temperature setting options for the homogenization section and the die are the same as described above and will not be described in detail herein.
According to the embodiment of the invention, when the film containing the vinylidene fluoride homopolymer or/and copolymer is prepared by using the single-layer film blowing method, the melt-shaped blank of the vinylidene fluoride homopolymer or/and copolymer film is extruded from the annular die, and the film can be prepared by controlling the draw ratio and the blow-up ratio. The traction ratio can be 0.8-25, preferably 2.0-15, and more preferably 3.0-10; the blow-up ratio may be 0.8 to 6.0, preferably 1.2 to 5.0, and more preferably 2.5 to 4.5.
According to the embodiment of the invention, when the film containing the vinylidene fluoride homopolymer or/and copolymer is prepared by using a multilayer film blowing method, taking an A/B/A three-layer co-extrusion film blowing as an example, the vinylidene fluoride homopolymer or/and copolymer is used as a B layer and is sandwiched between a protective layer resin A layer and extruded from an annular die, and the film can be prepared by controlling the traction ratio and the blow-up ratio. The traction ratio can be 0.8-35, preferably 2.0-25, and more preferably 2.0-15; the blow-up ratio may be 0.8 to 6.0, preferably 1.2 to 5.5, and more preferably 2.0 to 4.5.
According to an embodiment of the invention, the blow-up ratio is the stretch perpendicular to the film extrusion direction, i.e. the transverse direction; the draw ratio is the stretch in the extrusion direction of the film, i.e. the machine direction.
According to the embodiment of the invention, when the film containing the vinylidene fluoride homopolymer or/and copolymer is prepared by a multilayer casting method, taking A/B/A three-layer coextrusion casting as an example, the vinylidene fluoride homopolymer or/and copolymer is used as a B layer and is sandwiched between protective layer resin A layers and is extruded from a T-shaped die, and the thickness of the prepared film is 12-25 μm.
According to the embodiment of the invention, the protective layer is peeled off after the film is extruded from the die of the extruder by using the multilayer film blowing method or the multilayer casting method, so that the film containing the vinylidene fluoride homopolymer and/or copolymer can be obtained.
According to the embodiment of the invention, the film is prepared by a multilayer coextrusion method, and the advantages of introducing the protective layer are as follows: the protective layer is made of resin with better melt processing performance, so that the stability of film forming can be improved; the thickness of the vinylidene fluoride homopolymer or/and copolymer film in the middle layer can be further reduced, and the preparation of a thin film can be better realized.
According to an embodiment of the present invention, the protective layer resin includes one or more of: such as polyethylene, polypropylene, polybutylene, ethylene/acrylic acid copolymer, ethylene/methacrylic acid copolymer, ethylene/vinyl acetate copolymer, ethylene/vinyl alcohol copolymer, polyvinyl chloride, polystyrene, poly (4-methylpentene), polyethylene terephthalate, nylon, liquid crystal polymer, polyetheretherketone, polyphenylene sulfide, polyesteramide, polylactic acid, polybutylene adipate/terephthalate, polybutylene succinate, polyhydroxyalkanoate.
According to the embodiment of the invention, the preparation process flow of the vinylidene fluoride-containing homopolymer and/or copolymer film prepared by the melt extrusion method is simple, the product performance is uniform and stable, and the adhesion between the pole piece and the diaphragm is obviously improved.
According to the embodiment of the present invention, the step S102 of preparing the lithium ion battery composite separator further includes:
and (2) rolling the vinylidene fluoride-containing homopolymer and/or copolymer film prepared in the step (S101) into a roll sample by using a rolling machine or a winding drum, and performing hot-pressing cladding on the film and the polymer porous diaphragm in a roll-to-roll mode to obtain the lithium ion battery composite diaphragm.
According to an embodiment of the present invention, the thermal compression bonding with the polymer porous membrane in a roll-to-roll manner may include: laminating and hot-pressing a film layer containing a homopolymer and/or copolymer of vinylidene fluoride on one side of a polymer porous membrane layer; alternatively, a vinylidene fluoride-containing homopolymer and/or copolymer film layer is laminated and heat press-bonded on both sides of a polymeric porous separator layer.
For example, fig. 3 schematically illustrates a process for preparing a lithium ion battery composite separator by stacking a functional coating on one side of a polymer porous separator according to an embodiment of the present invention; fig. 4 schematically shows a process diagram for preparing a lithium ion battery composite separator by stacking functional coatings on both sides of a polymer porous separator according to an embodiment of the present invention.
In fig. 3 and 4, the unwinding mechanism 1 is used for driving the polymer porous membrane 2 to unwind and roll, the unwinding mechanism 3, the unwinding mechanism 31 and the unwinding mechanism 32 are used for driving the vinylidene fluoride-containing homopolymer or/and copolymer film 4 to unwind and roll, the preheating press roll set 5 is used for preheating and prepressing and laminating the polymer porous membrane 2 and the vinylidene fluoride-containing homopolymer or/and copolymer film 4, and the hot pressing system 6 is used for hot pressing and compounding and sizing the vinylidene fluoride-containing homopolymer or/and copolymer film and the polymer porous membrane.
Referring to fig. 3 and 4, under the traction of a winding guide roller 7, a polymer porous diaphragm 2 and a vinylidene fluoride homopolymer or/and copolymer-containing film 4 respectively enter a pre-hot pressing roller set 5 through an unwinding mechanism 1 and an unwinding mechanism 3 (or an unwinding mechanism 31 and an unwinding mechanism 32), and then the pre-heated and pre-pressed composite film enters a hot pressing system 6 to perform hot pressing compounding, hot setting, cooling setting and the like, so that a lithium ion battery composite diaphragm 8 in which a vinylidene fluoride homopolymer or/and copolymer-containing film is coated on one side surface of the polymer porous diaphragm 2 or a lithium ion battery composite diaphragm 9 in which a vinylidene fluoride homopolymer or/and copolymer-containing film is coated on both side surfaces of the polymer porous diaphragm 2 is finally obtained.
According to the embodiment of the present invention, the specific form and method of the hot pressing system 6 in the present invention are not particularly limited, as long as the apparatus and method can be used for hot press lamination of thin films.
According to the embodiment of the invention, the film containing vinylidene fluoride homopolymer or/and copolymer prepared by a melt extrusion method is rolled to prepare a roll film, and the steps of multi-step and multi-parameter control coating, drying and the like in the prior art are converted into a roll-to-roll hot press molding process, so that the molding efficiency and the uniformity and stability of the product performance are obviously improved; the prepared composite diaphragm can obviously improve the heat resistance and the pole piece adhesion of the polymer porous diaphragm.
The present invention also provides a lithium ion battery, comprising: the positive electrode, the negative electrode, the electrolyte and the lithium ion battery composite diaphragm prepared by the method.
According to an embodiment of the present invention, the lithium ion battery further includes, but is not limited to: the pole comprises a pole lug, a cover plate, a pole column, a safety valve and the like.
According to an embodiment of the present invention, a method of manufacturing a lithium ion battery includes: and placing the prepared lithium ion battery diaphragm between the anode and the cathode, filling electrolyte, and completing the preparation of the lithium ion battery containing the composite diaphragm through the process flows of vacuum packaging, standing, formation, shaping and the like. It should be noted that, there is no specific limitation on the preparation method of the lithium ion battery, and the lithium ion battery of the present invention can be prepared by any typical method in the prior art.
According to an embodiment of the present invention, the positive and negative electrodes of the lithium ion battery can be prepared in the form of an assembly of an electrode active material and a current collector, which are combined by typical methods and apparatuses used in the art.
According to the embodiment of the present invention, the positive electrode active material, the negative electrode active material, the current collector, the electrolyte, the lithium salt electrolyte, the organic compound solvent, and the additive of the lithium ion battery are not strictly limited, and may be any corresponding materials known in the art.
According to an embodiment of the present invention, the positive active material for a lithium ion battery may include lithium and lithium-containing composite metal oxides, including but not limited to layered oxide lithium cobaltate, layered oxide lithium nickelate, spinel-type lithium manganate, lithium iron phosphate, binary composite oxide, ternary composite oxide, and the like.
According to embodiments of the present invention, the negative active material for a lithium ion battery may include, but is not limited to, crystalline or amorphous carbon, or carbon-containing negative active material of a carbon composite, a burning polymer, carbon fiber, lithium metal, or alloys of lithium and other elements, metallic tin, oxides of tin, alloys of tin, and tin/carbon composite materials, silicon-based materials, transition metal oxides, and the like.
According to an embodiment of the present invention, a current collector for a lithium ion battery includes a positive electrode current collector and a negative electrode current collector. Wherein, the positive electrode current collector includes, but is not limited to, aluminum foil, nickel foil, combinations thereof, and the like; the negative current collector includes, but is not limited to, copper foil, gold foil, nickel foil, stainless steel foil, copper alloy foil, combinations thereof, and the like.
According to the embodiment of the invention, the electrolyte of the lithium ion battery can be obtained by combining three substances, namely a lithium salt electrolyte, an organic compound solvent and an additive.
Lithium salt electrolytes for lithium ion batteries according to embodiments of the present invention include, but are not limited to, lithium iron hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium trifluoromethylsulfonimide, and the like.
According to an embodiment of the present invention, the organic compound solvent for the lithium ion battery includes, but is not limited to, methyl propyl carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethylene carbonate, and the like.
According to the embodiment of the present invention, the additives for the lithium ion battery are to improve the interface property, increase the conductivity of the electrolyte, increase the flame retardant property, protect against overcharge, control the free water content in the electrolyte, and the like, and the additives used are not strictly limited.
According to the embodiment of the invention, the performance test of the composite diaphragm prepared by the method and the lithium ion battery containing the composite diaphragm comprises the following steps: thermal shrinkage, ionic conductivity, bond strength, and thermal stability.
According to an embodiment of the present invention, the heat shrinkage test comprises: and (3) shearing the prepared composite membranes into samples of 50mm multiplied by 50mm, preparing 5 samples for each composite membrane, keeping the samples at 120 ℃ for 1h, taking out, testing the sizes of the samples before and after shrinkage, and calculating to obtain the thermal shrinkage rate of the samples.
According to an embodiment of the present invention, the ion conductivity test comprises: and soaking the prepared composite diaphragm in electrolyte, and calculating the ionic conductivity of the composite diaphragm at 25 ℃.
According to an embodiment of the present invention, the bond strength test comprises: the prepared lithium ion batteries are disassembled and cut into samples of 15mm multiplied by 70mm, 5 samples are prepared for each lithium ion battery, the side of an electrode plate is bonded on a glass plate by using a double-sided adhesive tape, the bonding surface of a composite diaphragm and the electrode plate is uncovered from the edge, the composite diaphragm is peeled off in the direction of 90 degrees at the speed of 50mm/min, the peeling load is recorded by a digital display push-pull dynamometer, and the bonding strength is calculated according to the average value of the load in the peeling process.
According to an embodiment of the present invention, the thermal stability test comprises: the prepared lithium ion batteries are kept for 1h at the temperature range of 150 ℃ and 170 ℃, then whether short circuit occurs in the batteries is determined, 10 samples are prepared for each lithium ion battery, and the two conditions are respectively tested for 5 times.
The present invention is further illustrated in detail by the following specific examples. It should be noted that the present invention is not limited to these specific embodiments, and modifications and variations can be made to these specific embodiments based on the gist of the present invention, and the present invention is also within the scope of the present invention. Further, the chemicals and raw materials used in the following examples were either commercially available or self-prepared by a known preparation method.
Example 1
Weighing raw materials according to the proportion of 98wt% of vinylidene fluoride-hexafluoroethylene copolymer and 2 wt% of antioxidant, and putting the weighed raw materials into a high-speed mixer to mix for 0.5h at the speed of 4000 r/min. Wherein the vinylidene fluoride-hexafluoroethylene copolymer has a melting point T m The melt flow rate was 1.8g/10min at 145 ℃.
And putting the uniformly mixed materials into a double-screw extruder, and drying the obtained granules at the temperature of 60 ℃ for 1h at the speed of 300r/min to obtain the vinylidene fluoride-hexafluoroethylene copolymer-containing granules.
Putting the dried vinylidene fluoride-hexafluoroethylene copolymer-containing particles into a single-layer film blowing machine, wherein the temperature of a feeding section is 150 ℃, the temperature of a compression section is 170 ℃, the temperature of a homogenization section is 180 ℃, and the temperature of a neck mold is 170 ℃; the draw ratio was 6 and the inflation ratio was 2.7, and a vinylidene fluoride-hexafluoroethylene copolymer-containing film having a thickness of 12 μm was finally obtained.
And carrying out hot-pressing compounding on the prepared vinylidene fluoride-hexafluoroethylene copolymer-containing film and the polyethylene single-layer porous diaphragm according to a process diagram shown in figure 3 to obtain the composite diaphragm.
A positive electrode was prepared by appropriately coating a positive electrode material comprising 97 wt% of an active material, lithium cobalt oxide, 1.5 wt% of a conductive material, carbon black, and 1.5 wt% of a binder, polyvinylidene fluoride, on an aluminum foil; properly coating a negative electrode material containing 94 wt% of active material artificial graphite, 3 wt% of conductive material acetylene black and 3 wt% of binder styrene butadiene rubber on copper foil to prepare a negative electrode; an electrolyte was prepared by dissolving lithium hexafluorophosphate salt at a concentration of 1mol/L in an organic solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.
And stacking the prepared composite diaphragm, the positive plate and the negative plate according to the sequence of the positive electrode/the composite diaphragm/the negative electrode, then packaging in an aluminum bag, and carrying out baking, formation, secondary sealing, sorting and other steps during the period of properly injecting the electrolyte to prepare the lithium ion battery containing the composite diaphragm.
Example 2
The difference from example 1 is that the melting point T is selected m The melt flow rate of the vinylidene fluoride-hexafluoroethylene copolymer is 1.2g/10min at 165 ℃, the temperature of the feeding section of the single-layer film blowing machine is 175 ℃, the temperature of the compression section is 190 ℃, the temperature of the homogenization section is 200 ℃, and the temperature of the neck mold is 190 ℃.
Example 3
The difference from example 1 is that the melting point T is selected m At 165 deg.C, a melt flow rate of 1.2g/10min, drying the vinylidene fluoride-hexa-fluoroethylene copolymerPutting the vinyl fluoride copolymer particles into a three-layer co-extrusion film blowing machine, wherein the material of the protective layer is metallocene-catalyzed linear low-density polyethylene, the temperature of a feeding section is 175 ℃, the temperature of a compression section is 190 ℃, the temperature of a homogenization section is 200 ℃, and the temperature of a neck mold is 190 ℃.
Example 4
Weighing raw materials according to the proportion of 85 wt% of vinylidene fluoride-hexafluoroethylene copolymer, 10wt% of ceramic particles, 3 wt% of silane coupling agent and 2 wt% of antioxidant, and putting the weighed raw materials into a high-speed mixer to mix for 1h at the speed of 4000 r/min. Wherein the vinylidene fluoride-hexafluoroethylene copolymer has a melting point T m At 165 ℃ the melt flow rate was 1.2g/10 min; the ceramic particles are alumina particles having an average particle size of 100 nm.
And putting the uniformly mixed blend into a double-screw extruder to obtain particles containing the vinylidene fluoride-hexafluoroethylene copolymer at the speed of 500r/min, and drying the obtained particles for 1h at the temperature of 60 ℃.
Putting the dried vinylidene fluoride-hexafluoroethylene copolymer-containing particles into a single-layer film blowing machine, wherein the temperature of a feeding section is 170 ℃, the temperature of a compression section is 200 ℃, the temperature of a homogenization section is 210 ℃, and the temperature of a neck mold is 200 ℃; the draw ratio was 7 and the inflation ratio was 3.1, and a vinylidene fluoride-hexafluoroethylene copolymer-containing film having a thickness of 15 μm was finally obtained.
And carrying out hot-pressing compounding on the prepared vinylidene fluoride-hexafluoroethylene copolymer-containing film and the polyethylene single-layer porous diaphragm according to a process diagram shown in figure 4 to obtain the composite diaphragm.
A positive electrode was prepared by appropriately coating a positive electrode material comprising 97 wt% of an active material, lithium cobalt oxide, 1.5 wt% of a conductive material, carbon black, and 1.5 wt% of a binder, polyvinylidene fluoride, on an aluminum foil; properly coating a negative electrode material containing 94 wt% of active material artificial graphite, 3 wt% of conductive material acetylene black and 3 wt% of binder styrene butadiene rubber on copper foil to prepare a negative electrode; an electrolyte was prepared by dissolving lithium hexafluorophosphate salt at a concentration of 1mol/L in an organic solvent obtained by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1.
And stacking the prepared composite diaphragm, the positive plate and the negative plate according to the sequence of the positive electrode/the composite diaphragm/the negative electrode, then packaging in an aluminum bag, and carrying out baking, formation, secondary sealing, sorting and other steps during the period of properly injecting the electrolyte to prepare the lithium ion battery containing the composite diaphragm.
Example 5
The difference from the example 4 is that the raw materials are weighed according to the proportion of 80 wt% of vinylidene fluoride-hexafluoroethylene copolymer, 15 wt% of ceramic particles, 3 wt% of silane coupling agent and 2 wt% of antioxidant and are put into a high-speed mixer to be mixed for 1 hour at the speed of 4000 r/min.
Example 6
The difference from the example 4 is that the raw materials are weighed according to the proportion of 85 wt% of vinylidene fluoride-hexafluoroethylene copolymer, 10wt% of ceramic particles, 3 wt% of silane coupling agent and 2 wt% of antioxidant and are put into a high-speed mixer to be mixed for 1 hour at the speed of 4000 r/min.
And putting the uniformly mixed materials into a double-screw extruder at a speed of 500r/min to obtain particles containing the vinylidene fluoride-hexafluoroethylene copolymer, and drying the obtained particles for 1h at the temperature of 60 ℃.
Putting the dried vinylidene fluoride-hexafluoroethylene copolymer-containing particles into a five-layer co-extrusion casting machine, wherein the protective layer is made of high-density polyethylene, the temperature of a feeding section is 175 ℃, the temperature of a compression section is 210 ℃, the temperature of a homogenization section is 220 ℃, the temperature of a neck ring mold is 210 ℃, and finally the vinylidene fluoride-hexafluoroethylene copolymer-containing film with the thickness of 16 mu m is obtained.
Example 7
The difference from the example 4 is that the raw materials are weighed according to the proportion of 75 wt% of vinylidene fluoride-hexafluoroethylene copolymer, 20 wt% of ceramic particles, 3 wt% of silane coupling agent and 2 wt% of antioxidant and are put into a high-speed mixer to be mixed for 1 hour at the speed of 4000 r/min.
And putting the uniformly mixed materials into a double-screw extruder at a speed of 500r/min to obtain particles containing the vinylidene fluoride-hexafluoroethylene copolymer, and drying the obtained particles for 1h at the temperature of 60 ℃.
Putting the dried vinylidene fluoride-hexafluoroethylene copolymer-containing particles into a five-layer co-extrusion casting machine, wherein the protective layer is made of high-density polyethylene, the temperature of a feeding section is 175 ℃, the temperature of a compression section is 210 ℃, the temperature of a homogenization section is 220 ℃, the temperature of a neck ring mold is 210 ℃, and finally the vinylidene fluoride-hexafluoroethylene copolymer-containing film with the thickness of 17 mu m is obtained.
Example 8
Weighing raw materials according to the proportion of 85 wt% of vinylidene fluoride-hexafluoroethylene copolymer, 5 wt% of ceramic particles, 5 wt% of ethylene-vinyl acetate copolymer, 3 wt% of silane coupling agent and 2 wt% of antioxidant, and putting the weighed raw materials into a high-speed mixer to mix for 1h at the speed of 4000 r/min. Wherein the vinylidene fluoride-hexafluoroethylene copolymer has a melting point T m At 165 ℃ the melt flow rate was 1.2g/10 min; the ceramic particles are alumina particles having an average particle size of 100 nm.
And putting the uniformly mixed materials into a double-screw extruder at a speed of 500r/min to obtain particles containing the vinylidene fluoride-hexafluoroethylene copolymer, and drying the obtained particles for 1h at the temperature of 60 ℃.
Putting the dried vinylidene fluoride-hexafluoroethylene copolymer-containing particles into a three-layer co-extrusion film blowing machine, wherein the protective layer material is metallocene-catalyzed linear low-density polyethylene, the temperature of a feeding section is 170 ℃, the temperature of a compression section is 200 ℃, the temperature of a homogenization section is 210 ℃, and the temperature of a neck mold is 200 ℃; the draw ratio was 8 and the blow ratio was 2.7, to finally obtain a vinylidene fluoride-hexafluoroethylene copolymer film having a thickness of 15 μm.
And (3) carrying out hot-pressing compounding on the prepared vinylidene fluoride-hexafluoroethylene copolymer-containing film and the polyethylene single-layer porous diaphragm according to the process diagram shown in figure 4 to obtain the composite diaphragm.
A positive electrode was prepared by appropriately coating a positive electrode material comprising 97 wt% of an active material, lithium cobalt oxide, 1.5 wt% of a conductive material, carbon black, and 1.5 wt% of a binder, polyvinylidene fluoride, on an aluminum foil; a negative electrode was prepared by appropriately coating a copper foil with a negative electrode material containing 94 wt% of active material artificial graphite, 3 wt% of conductive material acetylene black and 3 wt% of binder styrene-butadiene rubber, and an electrolyte was prepared by dissolving lithium hexafluorophosphate in a concentration of 1mol/L in an organic solvent obtained by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1.
And stacking the prepared composite diaphragm, the positive plate and the negative plate according to the sequence of the positive electrode/the composite diaphragm/the negative electrode, then packaging in an aluminum bag, properly injecting electrolyte, baking, forming, secondary sealing, sorting and the like to prepare the lithium ion battery containing the composite diaphragm.
Table 1 shows the characterization results of the performance tests performed on the composite separator and the lithium ion battery containing the composite separator prepared in each of the above specific examples. As shown in table 1.
TABLE 1
Among them, in table 1 ∘: no short circuit was found in any of the 5 tests.
A tangle-solidup: short circuits were found to occur in 1 of 5 tests.
X: short circuits were found to occur more than 1 out of 5 tests.
By combining the above embodiments and the characterization results in table 1, it can be seen that the lithium ion battery composite separator provided by the invention has a lower thermal shrinkage rate and a higher room temperature ionic conductivity, and when the lithium ion battery composite separator is combined with an electrode, the separator and an electrode plate have excellent adhesion reliability, and the thermal stability and the use safety of a lithium ion battery containing the composite separator are improved. Comparing the embodiment 1 with the embodiment 2, the vinylidene fluoride-hexafluoropropylene copolymer with higher melting point is selected to further improve the heat resistance of the composite diaphragm and the safety of the lithium ion battery; particularly, in embodiments 4 to 7, the thermal safety of the lithium ion battery can be improved to 170 ℃ by using the lithium ion battery composite membrane provided by the invention; compared with the examples 2-3 and 4-5, the addition of the ceramic particles can improve the high-temperature dimensional stability of the diaphragm and simultaneously improve the ionic conductivity of the diaphragm; as can be seen from example 8, the adhesion of the composite separator can be further improved by adding a tackifying resin.
According to the embodiment of the invention, the heat resistance and the pole piece adhesion of the polymer porous diaphragm can be improved through the provided lithium ion battery composite diaphragm, the preparation method thereof and the lithium ion battery containing the composite diaphragm, and the safety of the lithium ion battery prepared by the lithium ion battery composite diaphragm can be improved.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are within the scope of the present invention.
Claims (8)
1. A lithium ion battery composite separator comprising: a polymeric porous separator layer and a vinylidene fluoride-containing homopolymer and/or copolymer film layer on at least one side of said polymeric porous separator layer;
the film layer containing the vinylidene fluoride homopolymer and/or copolymer is prepared by a melt extrusion method by using a composition containing the vinylidene fluoride homopolymer and/or copolymer, wherein the thickness of the film layer containing the vinylidene fluoride homopolymer and/or copolymer is 12-25 mu m;
the composition comprises the following components in percentage by weight: 65-98% of vinylidene fluoride homopolymer and/or copolymer, 5-25% of ceramic particles and 2-10% of modification auxiliary agent, wherein the modification auxiliary agent comprises tackifying resin, and the tackifying resin comprises at least one of the following components: polyacrylic acid, polymethacrylic acid, polymethylmethacrylate, polybutylmethacrylate, polyethylacrylate, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer;
melting point T of the vinylidene fluoride homopolymer and/or copolymer m The melt flow rate is 0.6-6.0 g/10min at 125-185 ℃.
2. The lithium ion battery composite separator of claim 1, wherein the polymeric porous separator layer comprises one of: polyethylene single-layer diaphragm, polypropylene/polyethylene/polypropylene multi-layer diaphragm, polyethylene/polypropylene/polyethylene multi-layer diaphragm, polytetrafluoroethylene diaphragm, polyamide diaphragm, polyimide diaphragm, cellulose diaphragm, polyethylene terephthalate diaphragm.
3. The lithium ion battery composite separator of claim 1, wherein the vinylidene fluoride homopolymer and/or copolymer comprises at least one of: polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-pentafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer.
4. The lithium ion battery composite separator of claim 1, wherein the ceramic particles comprise at least one of: alumina, silica, titania, zirconia, ceria, lithium aluminum titanium phosphate; the average particle size of the ceramic particles is 10-600 nm.
5. The lithium ion battery composite separator according to claim 1, wherein the modification aids further comprise processing aids comprising antioxidants and dispersants.
6. A preparation method of a lithium ion battery composite diaphragm comprises the following steps:
preparing a vinylidene fluoride homopolymer and/or copolymer-containing film from a blend containing 65-98 wt% of vinylidene fluoride homopolymer and/or copolymer, 5-25 wt% of ceramic particles and 2-10 wt% of a modification aid by a melt extrusion method;
sequentially stacking the vinylidene fluoride homopolymer and/or copolymer-containing film on at least one side of the polymer porous diaphragm and carrying out hot pressing to prepare the lithium ion battery composite diaphragm, wherein the thickness of the vinylidene fluoride homopolymer and/or copolymer-containing film is 12-25 mu m;
wherein the vinylidene fluoride homopolymer and/or copolymer has a melting point T m The temperature is 125-185 ℃, and the melt flow rate is 0.6-6.0 g/10 min; the modification auxiliary agent comprises tackifying resin, and the tackifying resin comprises at least one of the following components: polyacrylic acid, polymethacrylic acid, polymethylmethacrylate, polybutylmethacrylate, polyethylacrylate, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer.
7. The method of manufacturing of claim 6, wherein the melt extrusion process comprises one of: single layer film blowing method, multilayer film blowing method, single layer casting method, multilayer casting method, casting stretching method.
8. A lithium ion battery comprising: the lithium ion battery composite diaphragm is the lithium ion battery composite diaphragm as defined in any one of claims 1 to 5 or the lithium ion battery composite diaphragm prepared by the preparation method as defined in any one of claims 6 to 7.
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