CN104852004A - Secondary battery composite membrane, preparation method thereof and secondary battery - Google Patents

Abstract

The invention provides a secondary battery composite diaphragm, a preparation method thereof, and a secondary battery. The secondary battery composite separator includes an electrical insulation matrix layer and a conductive layer combined on the surface of the electrical insulation matrix layer, the conductive layer contains conductive material, and the thickness of the conductive layer is 5-50 μm. The preparation method of the secondary battery composite diaphragm includes preparing a dispersion liquid or slurry containing a conductive material, applying the dispersion liquid or slurry containing a conductive material to a conductive layer on the surface of an electrical insulating matrix, drying the composite diaphragm, and drying the composite diaphragm after drying and shaping. Diaphragm compaction treatment and other steps. The diaphragm of the secondary battery adopts the composite diaphragm of the secondary battery of the present invention. The composite diaphragm of the secondary battery of the invention can effectively intercept the electrode material falling off from the current collector. And make it continue to charge and discharge. The preparation method has high production efficiency and can be industrialized. The secondary battery has a long cycle life.

Description

Composite diaphragm for secondary battery, preparation method thereof, and secondary battery

technical field

The invention belongs to the technical field of secondary batteries, and in particular relates to a secondary battery composite diaphragm, a preparation method thereof, and a secondary battery.

Background technique

Lithium-ion secondary batteries have the advantages of high open circuit voltage, high specific capacity, and no memory effect. They are widely used in digital electronic products such as mobile phones, digital cameras, and notebook computers, and are gradually being applied to electric vehicles. , Smart grid and other large and medium-sized equipment. With the continuous expansion of the application range of lithium-ion secondary batteries, more and more attention has been paid to its safety performance and cycle life.

Lithium-ion secondary batteries are mainly composed of positive electrodes, negative electrodes, electrolytes, separators, casings and other parts. Among them, separator and electrode materials are one of the key components that determine the performance of lithium-ion batteries. In the actual application process of the battery, the cycle life is also a very important reference index for the performance of the lithium-ion battery, in addition to the safety and the charge-discharge rate.

For electrode materials, the research and development of a new generation of lithium-ion batteries focuses on increasing the energy density of batteries by using high specific capacity electrode materials. However, when using new high specific capacity electrode materials (such as silicon, metal oxide negative electrode materials and lithium-rich positive electrodes Material) in the lithium-ion battery system, due to the large volume change of the electrode material during the lithium-deintercalation process, it is easy to cause the electrode material to fall off from the current collector and fail, resulting in a rapid decline in battery capacity and a greatly reduced cycle life. At present, the main modification methods for this kind of materials are doping, compounding or nanometerization around the material itself. Although this can improve the performance of the material, it usually will greatly increase the preparation cost of the material or reduce the tap density of the material, which is difficult to apply large-scale industrial production.

For the separator material, its main function is to serve as a physical insulation barrier between the positive and negative electrodes to prevent the internal short circuit of the battery, and at the same time provide a path for the diffusion of ions in the electrolyte. The diaphragm material suitable for lithium-ion batteries needs to meet the following conditions: good ionic conductivity and high ion migration number, chemical stability and electrochemical stability to the electrolyte, good mechanical tensile properties and mechanical strength, Sufficient wettability to the electrolyte, etc.

According to the coexistence form of the separator and the electrolyte, the separators used in lithium-ion batteries can be divided into three categories: liquid porous separators, semi-liquid separators and all-solid separators. At present, most of the separators used in commercial lithium-ion batteries are liquid porous films, and the electrolyte exists in the pores of the separator in liquid form, which has high mechanical properties and chemical stability. The research methods for improving the liquid porous diaphragm mainly include: improving the liquid retention rate of the diaphragm by increasing the porosity of the diaphragm to reduce the internal resistance of the battery, improving the safety of the battery by regulating the closed cell temperature of the diaphragm, and improving the ionic conductivity of the diaphragm by compounding materials etc.; the main purpose is to improve battery safety and charge-discharge rate.

In order to improve the mechanical properties, lithium ion conductivity and liquid absorption rate of the diaphragm, there have been related researches and some achievements have been made. For example, an organic-inorganic composite diaphragm is disclosed. This composite diaphragm is composed of inorganic particles and polymers. The composition of the material, the inorganic particles are uniformly distributed in the polymer, and the obtained composite separator has good mechanical properties and lithium ion conductivity. At present, another lithium-ion battery separator with a cellulose fiber substrate is disclosed. This separator is made of high-temperature-resistant cellulose as the substrate and coated with an inorganic coating. It has good liquid absorption and liquid retention capacity and Excellent high temperature resistance.

Since the shedding of the electrode material is one of the main reasons for the reduction of the cycle stability of the existing secondary battery system, and the composite diaphragms reported in the prior art all use insulating materials as the composite layer material, although it can improve the strength of the diaphragm itself and absorb liquid. However, it cannot play the role of intercepting the shedding electrode material and making it continue to charge and discharge, so it cannot improve the battery cycle performance.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art, to provide a secondary battery composite diaphragm and its preparation method, aiming at solving the problem that the existing secondary battery diaphragm cannot intercept the fallen electrode material and make it continue to realize charging and discharging, and cannot Technical issues for improving battery cycle performance.

Another object of the present invention is to provide a secondary battery with good cycle performance.

In order to achieve the above-mentioned purpose of the invention, the technical solutions of the embodiments of the present invention are as follows:

A composite diaphragm for a secondary battery, which includes an electrically insulating matrix layer and a conductive layer combined on the surface of the electrically insulating matrix layer, the conductive layer contains conductive materials, and the thickness of the conductive layer is 5-50 μm.

And, a preparation method of a secondary battery composite separator, comprising the steps of:

Dispersing conductive materials and surfactants into liquid solvents to prepare conductive material dispersions, or adding conductive materials and binders to solvents to prepare conductive material slurries;

forming a conductive layer on the surface of the electrically insulating substrate with the conductive material dispersion to form a first composite diaphragm; or forming a conductive layer on the surface of the electrically insulating substrate with the conductive material slurry to form a second composite diaphragm; wherein, the The thickness of the conductive layer of the first composite diaphragm or the second composite diaphragm is 5-50 μm;

After the first composite diaphragm is washed or the second composite diaphragm is dried and shaped to form a third composite diaphragm;

Pressing the third composite diaphragm for compaction treatment.

And, a kind of secondary battery, it comprises positive electrode, negative electrode and the diaphragm that is arranged between positive electrode and negative electrode, and described diaphragm is above-mentioned secondary battery composite diaphragm or by the preparation method of above-mentioned secondary battery composite diaphragm The obtained secondary battery composite separator was prepared.

Compared with the prior art, the secondary battery composite separator of the present invention combines the conductive material on the surface of the electrically insulating matrix layer in a layer structure, so that the conductive layer is closely attached to the surface of the electrically insulating matrix layer, and on the one hand, it retains the electrical insulation. The better porosity of the insulating matrix allows the infiltration of the electrolyte and the diffusion of ions. On the other hand, the conductive layer is a closely stacked three-dimensional conductive grid structure, which can intercept the electrode material falling off from the current collector and adsorb it on the surface of the conductive material; This makes the conductive layer play a role similar to the current collector, so that the electrode material adsorbed on the conductive material can continue to charge and discharge, effectively preventing the rapid capacity decline of the battery due to the falling off of the electrode material. Improve battery cycle life. In addition, the electrically insulating matrix layer meets the conditions that ordinary battery separators should have. It acts as an insulating layer, impregnates the electrolyte, provides ion diffusion channels, etc., and also acts as a supporting base for the conductive layer to provide the mechanical strength required by the composite separator.

The preparation method of the above-mentioned secondary battery composite diaphragm can effectively combine the conductive layer on the surface of the electrically insulating matrix layer through the control of the conductive layer, and the tightly stacked three-dimensional conductive grid structure ensures the structural stability of the secondary battery composite diaphragm. Thereby effectively intercepting the electrode material falling off from the current collector. At the same time, the good porosity of the electrically insulating matrix is preserved, allowing the infiltration of electrolyte and the diffusion of ions. In addition, the conditions of the method are easy to control, the performance of the prepared secondary battery composite diaphragm is stable, the process is simple, the production efficiency is high, and the method can be produced industrially, thereby effectively reducing the production cost.

Since the above-mentioned secondary battery adopts the above-mentioned secondary battery composite diaphragm, the secondary battery has an excellent cycle life.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is a schematic structural view of a secondary battery composite separator according to an embodiment of the present invention;

2 is a flow chart of a method for preparing a secondary battery composite diaphragm according to an embodiment of the present invention;

3 is a schematic structural diagram of a button battery containing a secondary battery composite separator according to the embodiment of the present invention provided by Embodiment 1 of the present invention;

Fig. 4 is a graph of the capacity retention rate of a coin cell containing a secondary battery composite diaphragm provided in Example 1 of the present invention and a normal coin cell capacity retention rate; wherein, Fig. 4 a) is a graph of the capacity retention rate of a common coin cell in a comparative example; Fig. 4b) is a graph of the capacity retention rate of the button battery containing the secondary battery composite separator provided in Example 1 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The example of the present invention provides a secondary battery composite diaphragm that effectively intercepts the electrode material falling off from the current collector, and its structure is shown in FIG. 1 . The secondary battery composite diaphragm comprises an electrical insulation matrix layer 1 and a conductive layer 2 bonded to the surface of the electrical insulation matrix layer 1.

Wherein, the conductive layer 2 is bonded to the surface of the electrically insulating matrix layer 1 in a layer structure, so that the conductive layer 2 is closely attached to the surface of the electrically insulating matrix layer. On the one hand, the better porosity of the electrically insulating matrix is retained, allowing electrolysis The infiltration of liquid and the diffusion of ions. On the other hand, the conductive layer is a closely stacked three-dimensional conductive grid structure, which can intercept the electrode material falling off from the current collector and adsorb it on the surface of the conductive material; This makes the conductive layer play a role similar to the current collector, so that the electrode material adsorbed on the conductive material can continue to charge and discharge, effectively preventing the rapid capacity decline of the battery due to the falling off of the electrode material. Improve battery cycle life. In addition, the electrically insulating matrix layer meets the conditions that ordinary battery separators should have. It acts as an insulating layer, impregnates the electrolyte, provides ion diffusion channels, etc., and also acts as a supporting base for the conductive layer to provide the mechanical strength required by the composite separator.

In addition, the inventors found in the research process that when the thickness of the conductive layer 2 is controlled to be less than 5 μm, it cannot play the role of intercepting the falling electrode material; when the thickness of the conductive layer 2 is controlled to be greater than 50 μm, it will greatly increase the overall thickness of the separator Thickness, expanding the distance between the positive and negative electrodes, thereby impairing the rapid charge and discharge capability of the battery. Therefore, in the secondary battery composite separator of the embodiment of the present invention, the thickness of the conductive layer 2 is 5-50 μm. In a preferred embodiment, the conductive layer 2 has a thickness of 20-30 μm. In some specific embodiments, the thickness of the conductive layer 2 is 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm and so on.

It is a matter of course that the material forming the conductive layer 2 contains a conductive material, and the conductive material should be suitable for a secondary battery. In one embodiment, the conductive material in the conductive layer 2 is selected from at least one of graphite sheets, carbon nanotubes, graphene, carbon nanofibers, and carbon nanospheres. The selected conductive material not only has excellent conductivity, but more importantly, it can be effectively stacked on the surface of the electrically insulating matrix layer 1 to form a three-dimensional conductive grid structure, effectively intercepting the electrode material falling off from the current collector, and at the same time, It can also effectively retain the better porosity of the electrical insulation matrix 1 .

In order to provide structural stability between the conductive layer 2 and the electrically insulating matrix layer 1 , in one embodiment, the material of the conductive layer 2 further contains a binder. The inventor also found in the research process that the mass ratio of the binder to the conductive material is higher than 1:2, which will affect the conductivity of the conductive layer 2 and reduce its conductivity; when the mass ratio of the binder to the conductive material If it is lower than 1:5, it will affect the structural stability between the conductive 2 and the electrically insulating matrix layer 1, so that the bonding strength between the two becomes weaker. Therefore, in one embodiment, the mass ratio of the adhesive to the conductive material is 1: (2～5). In some specific embodiments, the mass ratio of the binder to the conductive material may be 1:2, 1:3, 1:4, 1:5.

In one embodiment, the binder is selected from polyvinylidene fluoride, polytetrafluoroethylene and the like. The selected binder can effectively enhance the stability of the connection between the conductive layer 2 and the surface of the electrically insulating matrix layer 1 without affecting the conductive performance of the conductive layer 2 .

On the basis of the above-mentioned embodiments, the electrically insulating matrix layer 1 satisfies the conditions required by ordinary battery separators, serves as an insulating layer, impregnates the electrolyte, provides ion diffusion paths, etc., and also serves as a supporting base for the conductive layer, providing a composite The required mechanical strength of the diaphragm. Therefore, the electrically insulating matrix layer 1 can be selected from conventional separators of secondary batteries. In one embodiment, the electrically insulating matrix layer 1 is selected from commercially available lithium-ion battery polymer separators, glass fiber separators, or common filter papers. In order to make the structure between the electrically insulating matrix layer 1 and the conductive layer 2 stronger, the selection of the electrically insulating matrix layer 1 matches the type of conductive material in the conductive layer 2 and the type of solvent used to prepare the conductive layer 2 . In one embodiment, when water is used as a solvent, since water has no wettability to commercial lithium-ion battery polymer separators, such polymer separators cannot be used, while glass fiber separators or ordinary filter paper can filter smoothly Conductive material in aqueous solution. In another embodiment, since the pore diameters of glass fiber membranes and common filter papers are much larger than those of commercially available polymer membranes, they cannot be used to filter conductive materials at the nanoscale, such as nano-carbon spheres. Therefore, the conductive The material is selected from at least one of graphite sheet, carbon nanotube, graphene and carbon nanofiber.

As can be seen from the above, the composite diaphragm of the secondary battery of the above-mentioned embodiment is through the synergistic effect of the electrically insulating matrix layer 1 and the conductive layer 2, so that the composite diaphragm of the secondary battery of the above-mentioned embodiment has a better porosity of the electrically insulating matrix, and at the same time, the conductive layer 2 The formed three-dimensional conductive grid structure can effectively intercept the electrode material falling off from the current collector and adsorb it on the surface of the conductive material, so that the electrode material adsorbed on the conductive material can continue to charge and discharge, effectively preventing the battery from being damaged by the electrode material. Rapid capacity decline due to shedding, improving battery cycle life.

Correspondingly, the embodiment of the present invention also provides a preparation method of the secondary battery composite separator described above. Please refer to Figure 2 for the process flow of the preparation method of the secondary battery composite diaphragm, and please refer to Figure 1 at the same time, which includes the following steps:

Step S01. Prepare a dispersion or slurry containing a conductive material:

Dispersing conductive materials and surfactants into liquid solvents to prepare conductive material dispersions, or adding conductive materials and binders to solvents to prepare conductive material slurries;

Step S02. Apply the dispersion or slurry containing the conductive material to the conductive layer on the surface of the electrically insulating substrate:

The conductive material dispersion prepared in step S01 is formed on the surface of the electrical insulating substrate 1 to form a conductive layer 2 to form a first composite diaphragm; or the conductive material slurry prepared in step S01 is formed on the surface of the electrical insulating substrate 1 to form a conductive layer 2 , forming a second composite diaphragm;

Step S03. drying and shaping the composite diaphragm:

Washing the first composite diaphragm prepared in step S02 or drying and shaping the second composite diaphragm prepared in step S02 to form a third composite diaphragm;

Step S04. Compacting the dried and shaped composite diaphragm:

Pressing the third composite diaphragm prepared in step S03 for compaction treatment.

Specifically, in the above step S01, when the conductive material is prepared into a dispersion, the surfactant is a technical problem to prevent the conductive material from being agglomerated due to electrostatic adsorption, resulting in uneven dispersion of the conductive material. In one embodiment, the mass ratio of the conductive material to the surfactant is (1-10):1, and in some specific embodiments, the mass ratio of the conductive material to the surfactant is 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. The mass ratio of the two within this range can effectively prevent the agglomeration of the conductive material, and can effectively prevent the residue of the surfactant in the finished product, thereby affecting the conductivity of the conductive layer.

In order to effectively prevent the agglomeration of conductive materials, in one embodiment, the surfactant is selected from macromolecule surfactants such as povidone and polyethylene glycol, and ionic surfactants such as cetyltrimethylammonium bromide. any one or a mixture of two or more.

In addition, in the prepared dispersion liquid, the mass percent concentration of the conductive material is 0.1-1%, preferably 0.1-0.5%. The dispersion liquid with this percentage concentration can cooperate with the dispersant to effectively prevent the agglomeration and sedimentation of the conductive material, and at the same time effectively ensure that the conductive material is closely stacked on the surface of the electrically insulating substrate to form a conductive layer 2 with a three-dimensional conductive grid structure.

In one embodiment, the liquid solvent used to prepare the dispersion is selected from one or a mixed solvent of two or more of water, ethanol, acetone, ethylene glycol, nitrogen methylpyrrolidone, and the like.

When preparing the slurry with the conductive material, in one embodiment, the conductive material and the binder are added into the solvent at a mass ratio of 1:(2-5) for mixing and dispersing treatment to form a uniform slurry material. In one embodiment, the type of the binder is as described above, such as polyvinylidene fluoride, polytetrafluoroethylene and the like. In an embodiment, the solvent used to prepare the slurry may be a solution that can effectively dissolve the binder, for example, in an embodiment, the solution may be nitrogen methyl pyrrolidone or the like. In addition, the concentration of the slurry can be adjusted according to the requirements of actual production.

In this step S01, whether it is preparing a dispersion or a slurry, in one embodiment, the material selected for the conductive agent is as described above, and it is selected from graphite sheets, carbon nanotubes, graphene, carbon nanofibers, and carbon nanospheres. at least one of the

In the above step S02, when the dispersion liquid is used to form the conductive layer 2, the method of forming the conductive layer 2 on the surface of the electrical insulating substrate 1 by the conductive material dispersion liquid can be filtering or sedimentation. Wherein, when the conductive layer 2 is formed by the filtration method, the electrically insulating matrix 1 is used as a filter membrane, and the dispersion liquid is flowed through the electrically insulating matrix 1 at a flow rate of 0.1 to 2.5 cm/min, so that the conductive material is trapped and deposited on the electrically insulating matrix. A conductive layer 2 is formed on the surface of 1.

When the conductive layer 2 is formed by the sedimentation method, the electrical insulating substrate 1 is fixed and laid flat in a horizontally placed container with a flat bottom, the dispersion liquid is poured into the container, and left to stand for 10 to 60 minutes until the conductive material settles to the electrical insulating substrate. After surface 1, the remaining solution is removed, thereby forming a conductive layer 2 on the surface of the electrically insulating substrate 1.

When slurry is used to form the conductive layer 2 , the slurry can be directly coated on the surface of the electrical insulation substrate 1 to form a film, such as by brushing, spraying and the like. In order to obtain a high-quality conductive layer 2, in one embodiment, the mass concentration of the conductive material in the conductive material slurry in the above step S01 is controlled at 0.1% to 0.2%.

In this step S02 , it does not matter whether the conductive layer 2 is formed by using a dispersion liquid or by using a slurry. In one embodiment, the process conditions should be controlled to control the thickness of the formed conductive layer 2 between 5-50 μm. It is preferably controlled between 20-30 μm.

In the above step S03, the purpose of washing the first composite membrane prepared in step S02 is to remove the solvent and surfactant remaining in the first composite membrane. In order to effectively remove the solvent and surfactant remaining in the first composite diaphragm, in one embodiment, the washing is treated with a detergent. In some specific embodiments, the detergent is selected from one of distilled water, ethanol, and acetone. Or use more than two kinds to deal with them separately. In addition, when choosing a detergent, the solubility of surfactants and liquid solvents relative to the detergent should be considered. If, for example, the surfactant povidone is not soluble in acetone, acetone cannot be used as a detergent when povidone is used as a surfactant. After washing treatment, the residual solvent and surfactant in the first composite separator are removed to ensure the conductivity of the conductive layer 2 and the stability of the closely stacked three-dimensional conductive grid structure. After washing, the first composite membrane is dried to remove detergent.

In this step S03, since the second composite diaphragm is formed by coating with slurry, it is enough to directly dry the second composite diaphragm to remove the solvent.

In order to ensure the stability of the three-dimensional conductive grid structure in the conductive layer 2 and improve the quality of the conductive layer 2, in one embodiment, the drying and shaping process conditions are 40-60 ° C under normal pressure for 24-48 hours, or 20 hours Vacuum drying at ~60°C for 6-12 hours. The drying temperature should not exceed 60°C.

In the above step S04 , the purpose of compacting the third composite diaphragm is to make the conductive layer 2 tightly and firmly bonded to the surface of the electrically insulating matrix layer 1 . Therefore, in one embodiment, the pressing pressure for compacting the third composite diaphragm is 5-30 MPa, preferably 10-20 MPa. The pressure time is 20-60S. Through the compaction treatment of the process conditions, the conductive layer 2 is closely and firmly combined on the basis of the surface of the electrically insulating matrix layer 1, so that the conductive layer 2 retains the better porosity and tight stacking of the electrically insulating matrix. Specific three-dimensional conductive grid structure.

Therefore, the preparation method of the above-mentioned secondary battery composite diaphragm can control the formation method of the conductive layer, so that the conductive layer is effectively combined on the surface of the electrically insulating matrix layer, and the closely stacked three-dimensional conductive grid structure ensures the stability of the secondary battery composite diaphragm. The structure is stable, thereby effectively intercepting the electrode material falling off from the current collector. At the same time, the good porosity of the electrically insulating matrix is preserved, allowing the infiltration of electrolyte and the diffusion of ions. In addition, the conditions of the method are easy to control, the performance of the prepared secondary battery composite diaphragm is stable, the process is simple, the production efficiency is high, and the method can be produced industrially, thereby effectively reducing the production cost.

Correspondingly, on the basis of the above-mentioned secondary battery composite separator and its preparation method, the embodiment of the present invention further provides a secondary battery, the secondary battery includes the above-mentioned secondary battery composite separator diaphragm. It is a matter of course that the secondary battery also includes other components necessary for lithium-ion batteries, such as positive electrodes, negative electrodes, and electrolytes. Since these other components are conventional, no details will be given here. In one embodiment, the secondary battery is a lithium ion battery.

In this way, since the secondary battery contains the above-mentioned secondary battery composite diaphragm, when the electrode material of the secondary battery expands and falls off during the process of deintercalating lithium ions, the secondary battery composite diaphragm can effectively intercept the electrode material, And it is adsorbed on the surface of the conductive layer 2, so that the electrode material and the conductive layer 2 can continue to charge and discharge the adsorbed electrode material, effectively prevent the rapid capacity decline of the battery, and improve the cycle life of the battery.

The secondary battery has a long battery cycle life. Therefore, the secondary battery such as a lithium ion battery can be used in communication equipment and electric vehicles, but is not limited to communication equipment and electric vehicles, and can also be used in other fields.

The above-mentioned secondary battery composite separator, its preparation method, performance of the secondary battery, and the like are illustrated below through a plurality of examples.

Example 1

A composite diaphragm for a secondary battery and a preparation method thereof. The structure of the secondary battery composite separator is shown in FIG. 1 . It comprises an electrically insulating matrix layer 1 and a conductive layer 2 combined on the surface of the electrically insulating matrix layer 1 . Wherein, the material of the electrically insulating matrix layer 1 is Celgard 2400 lithium-ion battery polymer diaphragm; the thickness of the conductive layer 2 is 20 μm, which includes carbon nanotubes as the conductive material.

The preparation method of the secondary battery composite diaphragm is as follows:

S11. Conductive material and povidone are added in dehydrated alcohol according to the ratio of mass ratio 5:1, carry out sufficient dispersion, be mixed with uniform conductive material dispersion liquid;

S12. The conductive material dispersion prepared in step S11 is filtered to flow through the electrical insulating matrix 1 at a flow rate of 0.2 cm/min, so that the conductive material is trapped on the surface of the electrical insulating matrix 1 to form a uniform conductive material layer 2. Composite diaphragm;

S13. washing the composite diaphragm prepared in step S12 with acetone and then vacuum-drying at 50° C. for 48 hours to finalize the shape, and removing residual surfactant and solvent in the composite diaphragm;

S14. Applying pressure to the composite diaphragm dried and shaped in step S13 for compaction to obtain a secondary battery composite diaphragm, wherein the pressure is set to 10 MPa, and the time is controlled to 30 s.

Example 2

A composite diaphragm for a secondary battery and a preparation method thereof. The structure of the secondary battery composite separator is shown in FIG. 1 . It comprises an electrically insulating matrix layer 1 and a conductive layer 2 combined on the surface of the electrically insulating matrix layer 1 . Wherein, the material of the electrically insulating matrix layer 1 is selected from Celgard 2400 polymer membrane; the thickness of the conductive layer 2 is 30 μm, which includes graphene as the conductive material and polyvinylidene fluoride as the binder, the conductive material and the binder The mass ratio is 4:1.

The preparation method of the secondary battery composite diaphragm is as follows:

S21. Add the conductive material and the binder into the nitrogen methyl pyrrolidone according to the mass ratio of 4:1, carry out sufficient mixing treatment, and prepare a uniform conductive material slurry;

S22. Coating the conductive material slurry prepared in step S21 on the surface of the electrical insulation matrix 1 to form a conductive layer 2 with uniform thickness;

S23. Dry the composite diaphragm prepared in step S22 at normal pressure at 60° C. for 24 hours to finalize the shape;

S24. Applying pressure to the composite separator dried and shaped in step S23 for compaction to obtain a secondary battery composite separator, wherein the pressure is set to 10 MPa, and the time is controlled to 30 seconds.

Example 3

A composite diaphragm for a secondary battery and a preparation method thereof. The structure of the secondary battery composite separator is shown in FIG. 1 . It comprises an electrically insulating matrix layer 1 and a conductive layer 2 combined on the surface of the electrically insulating matrix layer 1 . Wherein, the material of the electrically insulating matrix layer 1 is selected from cellulose filter paper; the thickness of the conductive layer 2 is 30 μm, and it includes a graphite sheet as a conductive material.

The preparation method of the secondary battery composite diaphragm is as follows:

S31. Add the conductive material and povidone into distilled water according to the mass ratio of 5:1, and fully disperse to form a conductive material dispersion;

S32. Fix the cellulose filter paper to the bottom of the flat-bottomed tank and place the tank horizontally; then pour the dispersion prepared in step S31 into the flat-bottomed tank, remove the solution in the tank after standing for 24 hours, and place it on the surface of the insulating matrix layer 1 forming a uniform conductive layer 2;

S33. Vacuum-dry the composite diaphragm prepared in step S32 at 50° C. for 48 hours to finalize the shape;

S34. Applying pressure to the composite separator dried and shaped in step S33 for compaction to obtain a secondary battery composite separator, wherein the pressure is set to 15 MPa, and the time is controlled to 40 s.

Example 4

A composite diaphragm for a secondary battery and a preparation method thereof. The structure of the secondary battery composite separator is shown in FIG. 1 . It comprises an electrically insulating matrix layer 1 and a conductive layer 2 combined on the surface of the electrically insulating matrix layer 1 . Wherein, the material of the electrically insulating matrix layer 1 is Celgard 2400 lithium-ion battery polymer diaphragm; the thickness of the conductive layer 2 is 5 μm, which includes nano-carbon spheres as the conductive material.

The preparation method of the secondary battery composite diaphragm is as follows:

S41. Add the conductive material and cetyltrimethylammonium bromide ionic surfactant to ethylene glycol according to the mass ratio of 10:1, fully disperse, and prepare a uniform conductive material dispersion;

S42. The conductive material dispersion prepared in step S41 is filtered to flow through the electrical insulating matrix 1 at a flow rate of 2.5 cm/min, so that the conductive material is trapped on the surface of the electrical insulating matrix 1 to form a uniform conductive material layer 2, making Composite diaphragm;

S43. washing the composite diaphragm prepared in step S42 with acetone and then vacuum-drying at 40° C. for 48 hours to finalize the shape to remove residual surfactant and solvent in the composite diaphragm;

S44. Applying pressure to the composite separator dried and shaped in step S43 for compaction to obtain a secondary battery composite separator, wherein the pressure is set to 30 MPa, and the time is controlled to 20 s.

Example 5

A composite diaphragm for a secondary battery and a preparation method thereof. The structure of the secondary battery composite separator is shown in FIG. 1 . It comprises an electrically insulating matrix layer 1 and a conductive layer 2 combined on the surface of the electrically insulating matrix layer 1 . Wherein, the material of the electrically insulating matrix layer 1 is a glass fiber diaphragm; the thickness of the conductive layer 2 is 50 μm, which includes a mixed conductive material of carbon nanofibers and graphite flakes at a mass ratio of 1:1.

The preparation method of the secondary battery composite diaphragm is as follows:

S51. Add the conductive material and cetyltrimethylammonium bromide ionic surfactant to ethylene glycol according to the mass ratio of 2:1, fully disperse, and prepare a uniform conductive material dispersion;

S52. The conductive material dispersion prepared in step S51 is filtered to flow through the electrical insulating matrix 1 at a flow rate of 0.2 cm/min, so that the conductive material is trapped on the surface of the electrical insulating matrix 1 to form a uniform conductive material layer 2, making Composite diaphragm;

S53. Washing the composite diaphragm prepared in step S52 with acetone and then vacuum-drying at 60° C. for 30 h to shape the composite diaphragm to remove residual surfactant and solvent in the composite diaphragm;

S54. Applying pressure to the composite separator dried and shaped in step S53 for compaction to obtain a secondary battery composite separator, wherein the pressure is set to 5 MPa, and the time is controlled to 30 s.

Secondary Battery Example

The secondary battery composite separators provided in the above embodiments were assembled according to conventional button lithium ion batteries, and the structure of the assembled button lithium ion battery is shown in FIG. 3 . The secondary battery composite diaphragm is laminated between the electrode and the lithium sheet of the button lithium ion battery, wherein the electrode includes a current collector 4 and an electrode material layer 3 bonded to the surface of the current collector 4, and the electrical conductivity of the secondary battery composite diaphragm is The layer 2 is laminated with the electrode material layer 3 of the electrode, and the electrically insulating matrix layer 1 is laminated with the lithium sheet 5 .

Secondary Battery Comparative Example

Lithium coin cells with conventional separators are available.

Performance Testing:

Each of the button-type lithium batteries prepared in the secondary battery example and the button-type lithium batteries with a common diaphragm in the comparative example were respectively subjected to a test experiment of capacity retention.

Wherein, the capacity retention rate test results of the button lithium battery prepared by the secondary battery composite diaphragm provided in Example 1 are shown in Figure 4b). The test results of the capacity retention rate of the button lithium battery with the common diaphragm in the comparative example are shown in FIG. 4a). Comparing Fig. 4a) and Fig. 4b), under the same conditions, the button lithium battery provided by the embodiment of the present invention has an obvious capacity retention rate in the charging and discharging process.

Through the test, the test results of the button lithium battery prepared by using the secondary battery composite separator provided in other embodiments are similar to those shown in FIG. 4 a ).

It can be seen that, on the basis of advantages such as good porosity and mechanical strength, the secondary battery composite diaphragm prepared by the present invention can intercept and drop off the electrode material from the current collector through the effect of the conductive layer 2, so that the electrode material It can continue to charge and discharge, effectively improving the cycle life of the secondary battery.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A secondary battery composite separator, which comprises an electrically insulating matrix layer and a conductive layer bonded to the surface of the electrically insulating matrix layer, the conductive layer comprises conductive material, and the thickness of the conductive layer is 5-50 μm . 2 . The composite separator for secondary battery according to claim 1 , wherein the conductive layer has a thickness of 20-30 μm. 3 . The composite diaphragm for secondary battery according to claim 1 , characterized in that: the conductive layer further contains a binder, and the mass ratio of the binder to the conductive material is 1:(2-5). 4. The secondary battery composite separator according to any one of claims 1 to 3, wherein the conductive material is selected from at least one of graphite sheets, carbon nanotubes, graphene, carbon nanofibers, and carbon nanospheres kind. 5 . The secondary battery composite separator according to any one of claims 1 to 3 , characterized in that: the material of the electrical insulating matrix layer is selected from any one of lithium ion battery polymer separators, glass fiber separators, and filter papers. 6. A preparation method for a secondary battery composite diaphragm, comprising the steps of: Dispersing conductive materials and surfactants into liquid solvents to prepare conductive material dispersions, or adding conductive materials and binders to solvents to prepare conductive material slurries; forming a conductive layer on the surface of the electrically insulating substrate with the conductive material dispersion to form a first composite diaphragm; or forming a conductive layer on the surface of the electrically insulating substrate with the conductive material slurry to form a second composite diaphragm; wherein, the The thickness of the conductive layer of the first composite diaphragm or the second composite diaphragm is 5-50 μm; After the first composite diaphragm is washed or the second composite diaphragm is dried and shaped to form a third composite diaphragm; Pressing the third composite diaphragm for compaction treatment. 7. The preparation method of the secondary battery composite diaphragm according to claim 7, characterized in that: the mass ratio of the conductive material to the surfactant is (1-10): 1; and/or The mass ratio of the conductive material to the binder is (2-5):1; and/or The mass concentration of the conductive material in the conductive material slurry is 0.1%˜0.2%. 8. The method for preparing a secondary battery composite diaphragm according to claim 6 or 7, characterized in that: the thickness of the conductive layer of the first composite diaphragm or the second composite diaphragm is 20-30 μm; and /or The surfactant is selected from any one or a mixture of two or more of povidone, polyethylene glycol polymer surfactant, cetyltrimethylammonium bromide ionic surfactant; and/ or In the step of preparing the first composite diaphragm, the electrical insulating matrix is used as a filter membrane, and the conductive material dispersion is flowed through the electrical insulating matrix at a flow rate of 0.1-2.5 cm/min, so that the conductive material is in the A conductive layer is formed on the surface of the electrically insulating substrate. 9 . The method for preparing a secondary battery composite separator according to claim 6 or 7 , characterized in that: the pressing pressure for compacting the third composite separator is 5-30 MPa, and the time is 10-100 seconds. 10. A secondary battery comprising a positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode, the separator being the secondary battery composite separator according to any one of claims 1 to 5 or by the The secondary battery composite separator prepared by the method for preparing the secondary battery composite separator described in any one of 6 to 9 is required.