Composite lithium ion battery separator, method for preparing the same, and lithium ion battery

Abstract

The application discloses a composite lithium ion battery diaphragm, a preparation method thereof and a lithium ion battery. The diaphragm comprises a base film and inorganic particles embedded in the base film and penetrating the base film at both ends. One end of the inorganic particles is coated with a nickel-lithium metal coating, and the other end is coated with a gradient nickel metal layer composed of a coarse-crystal plating layer and a fine-crystal plating layer. The preparation method comprises the following steps: melt blending to prepare a polymer base, forming a base film, rolling and embedding inorganic particles, metal conductive treatment, asymmetric electrochemical deposition to form different coatings on both sides, and extraction pore forming. The composite lithium ion battery diaphragm of the application utilizes the structure of different conductive coatings on both sides, can actively adjust lithium ion transmission, solves the problems of negative electrode lithium supplement and positive electrode lithium dissolution, and significantly improves the cycle life and capacity retention rate of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a composite lithium ion battery separator, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the rapid development of electric vehicles, energy storage devices and other fields, the performance requirements of lithium ion batteries are increasingly improved. In the electrochemical reaction process of lithium ion batteries, the problems of negative electrode lithium supplement and positive electrode lithium dissolution are one of the key factors affecting the performance and stability of the batteries.

[0003] The traditional lithium ion battery separator is relatively single in structure and function, and it is difficult to effectively solve the contradiction between negative electrode lithium supplement and positive electrode lithium dissolution. During the charging and discharging process of the battery, the negative electrode needs to supplement lithium ions to maintain its capacity and performance, while the positive electrode will have the phenomenon of lithium ion dissolution, which will lead to a series of problems such as battery capacity attenuation, cycle life shortening, and increased safety hazards. Therefore, it is of great practical significance to develop a new type of composite lithium ion battery separator that can effectively solve the above technical problems. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a composite lithium ion battery separator, a preparation method thereof and a lithium ion battery. The battery separator can effectively solve the problems of negative electrode lithium supplement and positive electrode lithium dissolution in the battery cycle process through a unique asymmetric conductive structure.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The present application provides a composite lithium ion battery separator, which comprises a base film and inorganic particles embedded in the base film, both ends of the inorganic particles penetrating through the two side surfaces of the base film, and one end surface of the inorganic particles being compounded and deposited with a nickel-lithium metal coating layer, and the other end surface of the inorganic particles being deposited with a nickel metal layer, wherein the nickel metal layer is a gradient structure composed of a coarse crystalline plating layer and a fine crystalline plating layer deposited outward from the surface of the base film.

[0007] In some embodiments, the material of the inorganic particles is one or more of alumina, silica, zirconia or boehmite, and the particle size of the inorganic particles is 1-5 μm.

[0008] In some embodiments, the material of the base film is at least two of polyethylene, polypropylene, polyvinylidene fluoride or polyimide.

[0009] In some embodiments, the thickness of the base film is 5-20 μm, the thickness of the nickel-lithium metal coating layer is 0.05-0.5 μm, and the total thickness of the nickel metal layer is 0.01-1 μm, wherein the thickness of the coarse crystalline coating layer accounts for at least one-third of the total thickness of the nickel metal layer.

[0010] In some embodiments, the composite lithium ion battery separator as a whole has a microporous structure formed by extraction pore formation, and the porosity is 30-70%.

[0011] The present application also provides a method for preparing the composite lithium ion battery separator, which comprises the following steps:

[0012] S1, a plurality of selected polymers are mixed according to a predetermined mass ratio and melt blended at a temperature of 180-220°C to form a composite eutectic base; specifically, at least two polymers are selected as base raw materials and mixed according to a predetermined mass ratio, and stirred and mixed at a temperature of 180-220°C to make the polymers fully fused to form a uniform composite eutectic base, wherein the predetermined mass ratio of any two polymers can be 1-3:1, and the stirring speed is 200-500 r / min.

[0013] S2, the composite eutectic base is formed into a base film by extrusion molding or casting molding, or the composite eutectic base is dissolved in a solvent to prepare a solution, and the solution is cast onto a substrate and dried to prepare a base film; the specific operation is as follows: the composite eutectic base is added to an extruder for extrusion, and after cooling and setting, a base film is obtained; or the composite eutectic base is dissolved in a solvent to prepare a corresponding solution, and then the solution is uniformly cast on a substrate by a casting machine, and after drying treatment, a base film is obtained.

[0014] S3, inorganic particles of a predetermined particle size are sprayed on the surface of the base film in a spraying manner, and the inorganic particles are inlaid into the base film by rolling, and both ends of the inorganic particles penetrate through the base film to obtain a first composite film;

[0015] S4, the first composite film is subjected to metal conductive treatment to form a metal conductive layer on the surface of the first composite film and the inorganic particles, thereby obtaining a second composite film, wherein the thickness of the metal conductive layer is 0.01-1 μm;

[0016] S5, performing one-way electrochemical deposition in an electrolyte containing nickel ions and lithium ions with the second composite film as a cathode and an insoluble anode as an anode, so that the first surface of the inorganic particles is deposited with a nickel-lithium composite metal coating in one direction, and then performing one-way electrochemical deposition in an electrolyte containing nickel ions with the second composite film as a cathode and a nickel plate as an anode, so that the second surface of the inorganic particles is deposited with a nickel metal layer in one direction, to obtain a third composite film, wherein the nickel metal layer has a gradient structure composed of a coarse-crystal plating layer and a fine-crystal plating layer deposited in sequence from the surface outward;

[0017] S6, performing extraction and pore-forming on the third composite film to obtain a composite lithium ion battery separator, specifically, first selecting an extractant such as xylene, dichloromethane, chloroform, etc., then immersing the third composite film in the selected extractant, adjusting the extraction temperature and extraction time, and then extracting part of the components in the third composite film to form a microporous structure, to obtain the composite lithium ion battery separator.

[0018] In some embodiments, in the step S3, the inorganic particles are rolled by a soft rubber roller to inlay the inorganic particles into the base film.

[0019] In some embodiments, in the step S4, the metal conductive treatment includes one of chemical plating, physical vapor deposition or chemical vapor deposition, and the conductive metal of the metal conductive treatment is one or more of nickel, cobalt, manganese, lithium and aluminum.

[0020] In some embodiments, in the step S5, the one-way deposition of the nickel metal layer on the second surface of the inorganic particles specifically includes: first depositing a coarse-crystal plating layer on the second surface of the inorganic particles by a large current density, then depositing a fine-crystal plating layer on the surface of the coarse-crystal plating layer by a small current density, and then forming a nickel metal layer having a gradient structure composed of the coarse-crystal plating layer and the fine-crystal plating layer.

[0021] The application also provides a lithium ion battery, which includes a positive electrode, a negative electrode and a composite lithium ion battery separator between the positive and negative electrodes, the composite lithium ion battery separator being the composite lithium ion battery separator described above or prepared by the preparation method described above, wherein the side of the composite lithium ion battery separator deposited with the nickel-lithium metal coating faces the positive electrode of the lithium ion battery, and the side of the composite lithium ion battery separator deposited with the nickel metal layer faces the negative electrode of the lithium ion battery.

[0022] Compared with the prior art, the application has the following beneficial technical effects:

[0023] (1) The present application constructs asymmetric metal conductive coating on both sides of the composite lithium ion battery separator, the nickel-lithium coating facing the positive electrode can act as a "lithium source", slowly releasing lithium ions during the cycle process to compensate for the irreversible lithium loss caused by the formation of the negative electrode SEI film (i.e. "lithium supplement"), at the same time, this structure helps to stabilize the positive electrode material interface and inhibit the dissolution of transition metals; the gradient nickel metal layer facing the negative electrode, its fine outer layer structure can evenly distribute the electric field and inhibit the growth of lithium dendrites, while the inner layer coarse crystalline structure ensures good electrical contact and mechanical support. This two-way adjustment function is not possessed by traditional homogeneous separators.

[0024] (2) The present application firmly anchors inorganic particles in the base film through the "rolling-inlaying" process, thereby forming a solid "rivet" structure throughout the separator, greatly enhancing the mechanical strength and puncture resistance of the separator and improving the safety of the battery.

[0025] (3) The present application combines the rolling-inlaying and gradient electrodeposition processes to avoid the problems of pore blockage and increased interface resistance caused by the use of adhesives in traditional coating processes, and the subsequent extraction pore-making also ensures that the separator has excellent and uniform ion conductivity.

[0026] (4) The present application applies the composite lithium ion battery separator to lithium ion batteries, which can significantly improve the capacity retention rate and cycle life of lithium ion batteries, and has better rate performance and safety, especially suitable for high-energy-density power batteries and long-life energy storage batteries. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0028] Figure 1 is a structure diagram of a composite lithium ion battery separator in the present application;

[0029] Figure 2 is a flow chart of a composite lithium ion battery separator preparation method in the present application;

[0030] Figure 3 is a cycle performance diagram of the battery assembled by example 1 and comparative example 1 after 100 charge-discharge cycles in the present application;

[0031] Figure 4is a contact angle test schematic diagram of the separator prepared in Example 1 and Comparative Example 1 of the present application, wherein 4a represents the contact angle result corresponding to the separator prepared in Comparative Example 1, and 4b represents the contact angle result corresponding to the separator prepared in Example 1.

[0032] Figure 5 is a nitrogen adsorption-desorption test isotherm diagram of the separator prepared in Example 1 and Comparative Example 1 of the present application, wherein 5a represents the nitrogen adsorption-desorption isotherm of the separator prepared in Example 1, Figure 5 b represents the nitrogen adsorption-desorption isotherm of the separator prepared in Comparative Example 1.

[0033] In the figure: 1. base film, 2. inorganic particles, 3. nickel-lithium metal coating, 4. nickel metal layer, 41. coarse crystalline plating layer, 42. fine crystalline plating layer. DETAILED DESCRIPTION

[0034] The present application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form.

[0035] As shown in Figure 1 The present application provides a composite lithium ion battery separator, which comprises a base film 1 and inorganic particles 2 embedded in the base film 1, both ends of the inorganic particles 2 penetrating through the two side surfaces of the base film 1, and one end surface of the inorganic particles 2 being compounded and deposited with a nickel-lithium metal coating 3, and the other end surface of the inorganic particles 2 being deposited with a nickel metal layer 4, wherein the nickel metal layer 4 is a gradient structure composed of a coarse crystalline plating layer 41 and a fine crystalline plating layer 42 deposited outward from the surface of the base film 1 in turn.

[0036] In the above embodiment, the material of the inorganic particles 2 is one or more of alumina, silica, zirconia or boehmite, and the particle size of the inorganic particles 2 is 1-5 μm.

[0037] In the above embodiment, the material of the base film 1 is at least two of polyethylene, polypropylene, polyvinylidene fluoride or polyimide.

[0038] In the above embodiment, the thickness of the base film 1 is 5-20 μm, the thickness of the nickel-lithium metal coating 3 is 0.05-0.5 μm, and the total thickness of the nickel metal layer 4 is 0.01-1 μm, wherein the thickness of the coarse crystalline plating layer 41 accounts for at least one third of the total thickness of the nickel metal layer 4.

[0039] In the above embodiment, the composite lithium ion battery separator as a whole has a microporous structure formed by extraction pore forming, and the porosity is 30-70%.

[0040] In the above embodiments, the asymmetric metal conductive coating is constructed on both sides of the composite lithium ion battery separator. By utilizing the different conductive coating structures on both sides, the lithium ion transmission can be actively adjusted, and the problems of anode lithium supplement and cathode lithium dissolution are solved. The nickel-lithium coating facing the cathode can act as a "lithium source" and slowly release lithium ions during the cycle process to compensate for the irreversible lithium loss caused by the formation of the anode SEI film. The gradient nickel metal layer 4 facing the anode has a fine and dense outer layer structure that can evenly distribute the electric field and inhibit the growth of lithium dendrites, while the inner layer of coarse crystalline structure ensures good electric contact and mechanical support. Therefore, the present application effectively solves the problems of anode lithium supplement and cathode lithium dissolution, and significantly improves the cycle life and capacity retention rate of lithium ion batteries.

[0041] As shown in Figure 2 The present application also provides a preparation method of a composite lithium ion battery separator, which is used to prepare the composite lithium ion battery separator described above, and comprises the following steps:

[0042] S1, mixing a plurality of selected polymers in a predetermined mass ratio, and melt blending under the condition of a temperature of 180-220 DEG C to form a composite eutectic matrix;

[0043] S2, extruding or casting the composite eutectic matrix to make a matrix film 1; or dissolving the composite eutectic matrix in a solvent to prepare a solution, and casting the solution onto a substrate to dry to make a matrix film 1;

[0044] S3, scattering inorganic particles 2 of a predetermined particle size on the surface of the matrix film 1, and embedding the inorganic particles 2 into the matrix film 1 by rolling, and the two ends of the inorganic particles 2 penetrating through the matrix film 1 to obtain a first composite film;

[0045] S4, performing a metal conductive treatment on the first composite film to form a metal conductive layer on the surface of the first composite film and the inorganic particles 2, and obtaining a second composite film;

[0046] S5, using the second composite film as a cathode, using an insoluble anode as an anode, and performing a one-way electrochemical deposition in an electrolyte containing nickel ions and lithium ions to make the first surface of the inorganic particles 2 deposit a nickel-lithium composite metal coating in one direction, and then using the second composite film as a cathode and a nickel plate as an anode to perform a one-way electrochemical deposition in an electrolyte containing nickel ions to make the second surface of the inorganic particles 2 deposit a nickel metal layer 4 in one direction, and obtaining a third composite film, wherein the nickel metal layer 4 is a gradient structure composed of a coarse crystalline plating layer 41 and a fine crystalline plating layer 42 deposited outward in sequence on the surface;

[0047] S6, performing extraction and pore making on the third composite film to obtain a composite lithium ion battery separator.

[0048] Based on the above description of the composite lithium-ion battery separator, the method for preparing the composite lithium-ion battery separator has the same beneficial technical effects, and will not be repeated here.

[0049] The present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a composite lithium-ion battery separator located between the positive and negative electrodes. The composite lithium-ion battery separator is the composite lithium-ion battery separator described above or the composite lithium-ion battery separator prepared by the preparation method described above. The side of the composite lithium-ion battery separator with the nickel-lithium metal coating 3 deposited faces the positive electrode of the lithium-ion battery, and the side with the nickel metal layer 4 deposited faces the negative electrode of the lithium-ion battery.

[0050] Based on the above description of the composite lithium-ion battery separator, when applied to a lithium-ion battery, the lithium-ion battery exhibits the same beneficial technical effects, which will not be elaborated further here.

[0051] To further illustrate the technical principles and effects of the present invention, several specific embodiments and comparative examples are provided below.

[0052] Example 1

[0053] (a) The specific steps for preparing the composite lithium-ion battery separator are as follows:

[0054] S1. Mix polyethylene (PE) and polypropylene (PP) with a thickness of 5μm at a mass ratio of 2:1, and stir at 300r / min at 200℃ until the polymers are fully fused to form a composite eutectic matrix.

[0055] S2. The above-mentioned composite eutectic matrix is ​​added to a twin-screw extruder for melt extrusion, and then shaped by cooling rollers to obtain matrix film 1;

[0056] S3. Alumina particles with an average particle size of 3μm are evenly spread on the surface of the substrate film 1. The alumina particles are rolled with a soft rubber roller with a Shore hardness of 60A so that the alumina particles are embedded in the substrate film 1 and the two ends of the alumina particles penetrate the substrate film 1 to obtain the first composite film.

[0057] S4. Using a chemical nickel plating process, the first composite film is immersed in a chemical plating solution with nickel sulfate as the main salt and sodium hypophosphite as the reducing agent to form a nickel conductive layer with a thickness of 0.1 μm on the surface of the first composite film and alumina particles, thereby obtaining the second composite film.

[0058] S5, one-way electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions, with the second composite film as the cathode and an insoluble anode as the anode; first, a nickel-lithium alloy coating with a thickness of 0.2 μm is co-deposited on the aluminum oxide particles on one side of the second composite film (the side facing the anode), then one-way electrochemical deposition is performed in an electrolyte containing nickel ions, with the second composite film as the cathode and a nickel plate as the anode, to sequentially deposit a coarse crystalline nickel layer (i.e., coarse crystalline plating layer 41) and a fine crystalline nickel layer (i.e., fine crystalline plating layer 42) on the aluminum oxide particles on the other side of the second composite film (the side facing the cathode) to form a nickel metal layer 4 with a gradient structure, thereby obtaining a third composite film, wherein the total thickness of the nickel metal layer 4 is 0.1 μm; it should be noted that the electrochemical deposition of the nickel-lithium alloy coating and the nickel metal layer 4 with a gradient structure are both prior art and will not be described in detail here;

[0059] S6, the third composite film is immersed in xylene for extraction to remove part of the soluble polymer components on the third composite film, thereby forming a microporous structure with a porosity of 45%, and after drying, the final composite lithium ion battery separator is obtained.

[0060] (II) Lithium ion battery assembly

[0061] NCM811 is used as the positive electrode active material and graphite is used as the negative electrode active material, and the positive electrode sheet and the negative electrode sheet are prepared according to the conventional process, the composite lithium ion battery separator prepared is placed between the positive and negative electrode sheets, one side of which is deposited with a nickel-lithium alloy coating and the other side of which is deposited with a gradient nickel metal layer 4, a carbonate electrolyte with a conventional lithium salt concentration of 1.0 M is injected, and a 2032 type button cell is packaged.

[0062] Example 2

[0063] (I) The composite lithium ion battery separator is prepared according to the following specific steps:

[0064] S1, polyethylene (PE) and polypropylene (PP) with a thickness of 10 μm are mixed in a mass ratio of 1:1, stirred at a speed of 200 r / min at 180℃ until the polymers are fully fused to form a composite co-melting matrix;

[0065] S2, the above composite co-melting matrix is added to a twin-screw extruder for melt extrusion, and is shaped by a cooling roller to obtain a matrix film 1;

[0066] S3, aluminum oxide particles with an average particle size of 1 μm are uniformly spread on the surface of the matrix film 1, and a soft rubber roller with a Shore hardness of 60A is used to roll the aluminum oxide particles to embed the aluminum oxide particles into the matrix film 1, and the two ends of the aluminum oxide particles penetrate the matrix film 1 to obtain a first composite film;

[0067] S4, using a chemical nickel plating process, the first composite film is immersed in a chemical plating solution with nickel sulfate as the main salt and sodium hypophosphite as the reducing agent, to form a 0.01 μm thick nickel conductive layer on the surface of the first composite film and the alumina particles, obtaining a second composite film;

[0068] S5, with the second composite film as the cathode and an insoluble anode as the anode, one-way electrochemical deposition is carried out in an electrolyte containing nickel ions and lithium ions; first, a 0.05 μm thick nickel-lithium alloy coating is co-deposited on the alumina particles on one side of the second composite film (the side facing the anode), then, with the second composite film as the cathode and a nickel plate as the anode, one-way electrochemical deposition is carried out in an electrolyte containing nickel ions, and a coarse crystalline nickel layer and a fine crystalline nickel layer are sequentially deposited on the alumina particles on the other side of the second composite film (the side facing the cathode) to form a gradient structured nickel metal layer 4, thereby obtaining a third composite film, wherein the total thickness of the nickel metal layer 4 is 0.01 μm;

[0069] S6, the third composite film is immersed in xylene for extraction, to remove part of the soluble polymer components on the third composite film, thereby forming a microporous structure with a porosity of 30%, and after drying, the final composite lithium ion battery separator is obtained.

[0070] (II) Lithium ion battery assembly

[0071] With NCM811 as the positive active material and graphite as the negative active material, the positive and negative electrode sheets are prepared according to the conventional process, the composite lithium ion battery separator prepared is placed between the positive and negative electrode sheets, wherein the side with the deposited nickel-lithium alloy coating is tightly attached to the positive electrode sheet, and the side with the deposited gradient nickel metal layer 4 is tightly attached to the negative electrode sheet, a carbonic acid electrolyte with a conventional lithium salt concentration of 1.0 M is injected, and a 2032 type button cell is packaged.

[0072] Example 3

[0073] (I) The composite lithium ion battery separator is prepared, and the specific steps are as follows:

[0074] S1, polyethylene (PE) and polypropylene (PP) with a thickness of 20 μm are mixed in a mass ratio of 3:1, stirred at a speed of 500 r / min at 220°C until the polymers are fully fused, forming a composite co-melt matrix;

[0075] S2, the above composite co-melt matrix is added to a twin-screw extruder for melt extrusion, and is shaped by a cooling roller to obtain a matrix film 1;

[0076] S3, uniformly spreading alumina particles with an average particle size of 5 μm on the surface of the base film 1, and using a soft rubber roller with a Shore hardness of 60A to roll the alumina particles so as to embed the alumina particles into the base film 1, and the two ends of the alumina particles penetrate through the base film 1, to obtain a first composite film;

[0077] S4, using a chemical nickel plating process, immersing the first composite film into a chemical plating solution taking nickel sulfate as a main salt and sodium hypophosphite as a reducing agent, to form a nickel conductive layer with a thickness of 0.01 μm on the surface of the first composite film and the alumina particles, to obtain a second composite film;

[0078] S5, using the second composite film as a cathode and an insoluble anode as an anode, performing one-way electrochemical deposition in an electrolyte containing nickel ions and lithium ions; first, co-depositing a nickel-lithium alloy coating layer with a thickness of 0.5 μm on the alumina particles on one side (the side facing the anode) of the second composite film, and then using the second composite film as a cathode and a nickel plate as an anode, performing one-way electrochemical deposition in an electrolyte containing nickel ions, and sequentially depositing a coarse crystalline nickel layer and a fine crystalline nickel layer on the alumina particles on the other side (the side facing the cathode) of the second composite film to form a nickel metal layer 4 with a gradient structure, thereby obtaining a third composite film, wherein the total thickness of the nickel metal layer 4 is 1 μm;

[0079] S6, immersing the third composite film into xylene for extraction, removing part of the soluble polymer components on the third composite film, and forming a microporous structure with a porosity of 70%, and obtaining a final composite lithium ion battery separator after drying.

[0080] (II) Lithium ion battery assembly

[0081] Using NCM811 as a positive electrode active material and graphite as a negative electrode active material, and preparing positive electrode sheets and negative electrode sheets according to a conventional process, placing the prepared composite lithium ion battery separator between the positive and negative electrode sheets, wherein the side with the deposited nickel-lithium alloy coating layer is in close contact with the positive electrode sheet, and the side with the deposited gradient nickel metal layer 4 is in close contact with the negative electrode sheet, injecting a carbonate electrolyte with a conventional lithium salt concentration of 1.0 M, and packaging into a 2032 type button cell.

[0082] Comparative Example 1

[0083] Comparative Example 1 is assembled according to the same method as Example 1, except that a commercially available separator with the same thickness as the composite lithium ion battery separator prepared in Example 1 is used.

[0084] Performance test

[0085] (1) The batteries assembled in Example 1 and Comparative Example 1 are tested for charge and discharge cycling under the same conditions, and the test is repeated for 100 times, as shown in Table 1. Figure 3 Table 1Figure 3 The middle line 1 shows the cycle performance results of the battery assembled by the composite lithium ion battery separator of the present application after 100 charge-discharge cycles, Figure 3 The middle line 2 shows the cycle performance results of the battery assembled by the composite lithium ion battery separator of the present application after 100 charge-discharge cycles, Figure 3 It can be seen that the capacity of the battery assembled by the composite lithium ion battery separator of the present application (Example 1) is still maintained at more than 96% after 100 charge-discharge cycles, because the composite lithium ion battery separator provided by the present application has the effects of lithium supplement and nickel layer inhibition, thereby significantly improving the capacity retention rate and cycle life of the lithium ion battery.

[0086] (2) The separator prepared in Example 1 and Comparative Example 1 was used as the battery separator, mixed with the positive active material LiCoO2, the conductive agent and the binder PVDF in a mass ratio of 8:1:1 to form a slurry, then uniformly coated on an aluminum foil with a medical spatula, naturally dried, and then punched into a round sheet (diameter 12 mm), dried at 105°C under vacuum (133 Pa) for 10 h to obtain an electrode sheet (active material content 3 mg). A CR2032 button cell was assembled in an argon-filled glove box with a lithium sheet as the negative electrode and 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) as the electrolyte, then a contact angle test was performed at 25°C, the test voltage was 2.0-4.5V, and the test results are shown in Figure 4 , Figure 4 a shows the contact angle results of the separator prepared in Comparative Example 1, Figure 4 b shows the contact angle results of the separator prepared in Example 1, from Figure 4 It can be seen that the contact angle of the separator prepared in Example 1 is significantly greater than that of Comparative Example 1, and the greater the contact angle, the better the wettability, i.e. the separator prepared in Example 1 has better electrolyte wettability, and after the separator with good electrolyte wettability contacts with the electrolyte, the good electrolyte wettability can ensure complete electrolyte wettability and increase the retention time of the electrolyte in the separator. Therefore, the separator prepared in Example 1 is beneficial to increasing the cycle life of the battery.

[0087] (3) The nitrogen adsorption-desorption test was performed on the separators prepared in Example 1 and Comparative Example 1, and the test results are shown in Figure 5 , Figure 5 a shows the nitrogen adsorption-desorption isotherm of the separator prepared in Example 1, Figure 5 b shows the nitrogen adsorption-desorption isotherm of the separator prepared in Comparative Example 1, from Figure 5As can be seen, the isotherms of Comparative Example 1 and Example 1 are both I-V type curves, and an H3 type hysteresis loop exists. This indicates that the membranes prepared in Comparative Example 1 and Example 1 both contain mesoporous structures. Figure 5 The nitrogen adsorption-desorption isotherm was obtained and calculated using the Brunauer-Emmett-Teller (BET) formula. The specific surface area corresponding to the membrane prepared in Example 1 was 173.855 m². 2 ·g -1 The specific surface area of ​​the diaphragm prepared in Comparative Example 1 is 156.429 m². 2 ·g -1 The pore volume of the diaphragm prepared in Example 1 is 0.672 cm³. 3 ·g -1 The pore volume of the diaphragm prepared in Comparative Example 1 is 0.496 cm³. 3 ·g -1 Therefore, it can be seen that the specific surface area and pore volume of the diaphragm prepared in Example 1 are both greater than those of Comparative Example 1.

[0088] (4) The batteries assembled in Examples 1-3 and Comparative Example 1 were subjected to 1C rate charge-discharge cycle tests under the same conditions. The test results are shown in Table 1.

[0089] Table 1. Charge-discharge cycle test results of batteries assembled in Examples 1-3 and Comparative Example 1

[0090] Example 1 Example 2 Example 3 Comparative Example 1 Battery capacity retention rate (%) after 500 cycles 95 94 92 76

[0091] As can be seen from Table 1, the battery capacity retention rate of Examples 1-3 after 500 cycles is all above 92%, while the battery capacity retention rate of Comparative Example 1 after 500 cycles is only 76%. This shows that the composite lithium-ion battery separator in this invention effectively alleviates the battery capacity decay.

[0092] The foregoing has provided a detailed description of a composite lithium-ion battery separator, its preparation method, and the lithium-ion battery itself. Specific examples have been used to illustrate the principles and implementation methods of this application; the descriptions of these embodiments are merely for the purpose of helping to understand the core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A composite lithium-ion battery separator, characterized by, The composite lithium-ion battery separator comprises a base film and inorganic particles embedded in the base film, both ends of the inorganic particles penetrating the two surfaces of the base film, and a nickel-lithium metal coating deposited on one end surface of the inorganic particles, and a nickel metal layer deposited on the other end surface of the inorganic particles, wherein the nickel metal layer is a gradient structure composed of a coarse crystalline plating layer and a fine crystalline plating layer deposited outward from the surface of the base film.

2. The composite lithium-ion battery separator according to claim 1, wherein, The inorganic particles are made of one or more of alumina, silica, zirconia, or boehmite, and the particle size of the inorganic particles is 1-5 μm.

3. The composite lithium-ion battery separator of claim 1, wherein, The base film is made of at least two of polyethylene, polypropylene, polyvinylidene fluoride, or polyimide.

4. The composite lithium-ion battery separator of claim 1, wherein, The thickness of the base film is 5-20 μm, the thickness of the nickel-lithium metal coating is 0.05-0.5 μm, and the total thickness of the nickel metal layer is 0.01-1 μm, wherein the thickness of the coarse crystalline plating layer accounts for at least one-third of the total thickness of the nickel metal layer.

5. The composite lithium-ion battery separator of claim 1, wherein, The composite lithium-ion battery separator as a whole has a microporous structure formed by extraction pore formation, and the porosity is 30-70%.

6. A method of preparing a composite lithium-ion battery separator, characterized by, The method for preparing the composite lithium-ion battery separator as claimed in any one of claims 1-5 comprises the following steps: S1, mixing a plurality of selected polymers in a predetermined mass ratio and melt blending at a temperature of 180-220 ℃ to form a composite co-melting base; S2, forming a base film by extrusion molding or casting molding of the composite co-melting base, or dissolving the composite co-melting base in a solvent to prepare a solution, and casting the solution onto a substrate to dry to form a base film; S3, spraying inorganic particles of a predetermined particle size onto the surface of the base film in a spraying manner, and embedding the inorganic particles into the base film by rolling, and both ends of the inorganic particles penetrating the base film to obtain a first composite film; S4, performing metal conductive treatment on the first composite film to form a metal conductive layer on the surface of the first composite film and the inorganic particles to obtain a second composite film; S5, using the second composite film as a cathode, using an insoluble anode as an anode, and performing one-way electrochemical deposition in an electrolyte containing nickel ions and lithium ions to deposit a nickel-lithium composite metal coating on the first surface of the inorganic particles, and then using the second composite film as a cathode and a nickel plate as an anode to perform one-way electrochemical deposition in an electrolyte containing nickel ions to deposit a nickel metal layer on the second surface of the inorganic particles to obtain a third composite film, wherein the nickel metal layer is a gradient structure composed of a coarse crystalline plating layer and a fine crystalline plating layer deposited outward from the surface; S6, performing extraction pore formation on the third composite film to obtain a composite lithium-ion battery separator.

7. The preparation method according to claim 6, characterized in that, In step S3, a soft rubber roller is used to roll the inorganic particles to embed them into the base film.

8. The preparation method according to claim 6, characterized in that, In step S4, the metal conductive treatment includes one of electroless plating, physical vapor deposition, or chemical vapor deposition, and the conductive metal of the metal conductive treatment is one or more of nickel, cobalt, manganese, lithium, and aluminum.

9. The preparation method according to claim 6, characterized in that, The step S5 of depositing a nickel metal layer on the second surface of the inorganic particle in one direction specifically includes: depositing a coarse-crystal plating layer on the second surface of the inorganic particle by a large current density, then depositing a fine-crystal plating layer on the surface of the coarse-crystal plating layer by a small current density, and further forming a nickel metal layer with a gradient structure composed of the coarse-crystal plating layer and the fine-crystal plating layer.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode, a negative electrode and a composite lithium ion battery separator between the positive and negative electrodes, the composite lithium ion battery separator being the composite lithium ion battery separator according to any one of claims 1 to 5 or prepared by the preparation method according to any one of claims 6 to 9, wherein the side of the composite lithium ion battery separator on which the nickel-lithium metal coating is deposited faces the positive electrode of the lithium ion battery, and the side of the composite lithium ion battery separator on which the nickel metal layer is deposited faces the negative electrode of the lithium ion battery.

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