Composite lithium ion battery diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention discloses a composite lithium ion battery diaphragm and a preparation method thereof and a lithium ion battery, the diaphragm comprises a matrix film and inorganic particles embedded in the matrix film, two ends of the inorganic particles penetrate through the matrix film, and a nickel-lithium metal coating is compositely deposited at one end of each inorganic particle. And a gradient nickel metal layer consisting of a coarse crystal coating and a fine crystal coating is deposited at the other end of the metal layer. The preparation method comprises the following steps: preparing a polymer matrix by melt blending, forming a matrix film, rolling and inlaying inorganic particles, performing metal conductive treatment, performing asymmetric electrochemical deposition to form different coatings on two sides, and extracting to form pores. According to the composite lithium ion battery diaphragm, different conductive coating structures on the two surfaces are utilized, lithium ion transmission can be actively adjusted, meanwhile, the problems of negative electrode lithium supplement and positive electrode lithium dissolution are solved, the cycle life of a battery is remarkably prolonged, and the capacity retention rate of the battery is remarkably increased.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite lithium-ion battery separator, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles, energy storage devices, and other fields, the performance requirements for lithium-ion batteries are increasing. In the electrochemical reaction process of lithium-ion batteries, the issues of lithium replenishment at the negative electrode and lithium dissolution at the positive electrode are among the key factors affecting battery performance and stability.

[0003] Traditional lithium-ion battery separators are relatively simple in structure and function, making it difficult to effectively resolve the contradiction between lithium replenishment at the negative electrode and lithium dissolution at the positive electrode. During battery charging and discharging, the negative electrode needs to be replenished with lithium ions to maintain its capacity and performance, while the positive electrode experiences lithium ion dissolution. This leads to a series of problems such as battery capacity decay, shortened cycle life, and increased safety hazards. Therefore, developing a novel composite lithium-ion battery separator that can effectively solve the above-mentioned technical problems is of significant practical importance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a composite lithium-ion battery separator, its preparation method, and a lithium-ion battery. This battery separator, through its unique asymmetric conductive structure, effectively solves the problems of lithium replenishment at the negative electrode and lithium dissolution at the positive electrode during battery cycling.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a composite lithium-ion battery separator, which includes a substrate film and inorganic particles embedded in the substrate film. The two ends of the inorganic particles penetrate the two sides of the substrate film, and a nickel-lithium metal coating is deposited on one end surface of the inorganic particles, while a nickel metal layer is deposited on the other end surface of the inorganic particles. The nickel metal layer is a gradient structure consisting of a coarse crystalline coating and a fine crystalline coating deposited sequentially from the surface of the substrate film.

[0006] In some embodiments, the inorganic particles are made of one or more of alumina, silicon dioxide, zirconium oxide, or boehmite, and the particle size of the inorganic particles is 1μm-5μm.

[0007] In some embodiments, the substrate film is made of at least two of polyethylene, polypropylene, polyvinylidene fluoride, or polyimide.

[0008] In some embodiments, the thickness of the substrate film is 5μm-20μm, the thickness of the nickel-lithium metal coating is 0.05μm-0.5μm, and the total thickness of the nickel metal layer is 0.01μm-1μm, wherein the thickness of the coarse crystal coating accounts for at least one-third of the total thickness of the nickel metal layer.

[0009] In some embodiments, the composite lithium-ion battery separator has an overall microporous structure formed by extraction pore creation, with a porosity of 30%-70%.

[0010] The present invention also provides a method for preparing a composite lithium-ion battery separator, the method being used to prepare the above-mentioned composite lithium-ion battery separator, comprising the following steps: S1. Mix the selected polymers according to a preset mass ratio and melt blend them at a temperature of 180℃-220℃ to form a composite eutectic matrix. Specifically, select at least two polymers as matrix raw materials and mix them according to a preset mass ratio. Stir and mix them at a temperature of 180℃-220℃ to fully fuse the polymers and form a uniform composite eutectic matrix. The preset mass ratio of any two polymers can be 1-3:1, and the stirring speed is 200-500 r / min.

[0011] S2. The composite eutectic matrix is ​​extruded or cast to form a substrate film; or, the composite eutectic matrix is ​​dissolved in a solvent to prepare a solution, and the solution is cast onto a substrate and dried to form a substrate film; specifically, the composite eutectic matrix is ​​added to an extruder and extruded, and after cooling and shaping, a substrate film is obtained; or, the composite eutectic matrix is ​​dissolved in a solvent to prepare a corresponding solution, and then the solution is uniformly cast onto a substrate using a casting machine, and after drying, a substrate film is obtained.

[0012] S3. Inorganic particles of a preset particle size are sprayed onto the surface of the substrate film by spraying. The inorganic particles are then embedded into the substrate film by rolling, with both ends of the inorganic particles penetrating the substrate film to obtain the first composite film. S4. Perform metal conductivity 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, wherein the thickness of the metal conductive layer is 0.01μm-1μm. S5. Using the second composite film as the cathode and the insoluble anode as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions, so that a nickel-lithium composite metal coating is unidirectionally deposited on the first surface of the inorganic particles. Then, using the second composite film as the cathode and the nickel plate as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions, so that a nickel metal layer is unidirectionally deposited on the second surface of the inorganic particles, to obtain a third composite film, wherein the nickel metal layer is a gradient structure consisting of a coarse crystal coating and a fine crystal coating deposited sequentially from the surface outward. S6. Extract and create pores in the third composite film to obtain a composite lithium-ion battery separator. Specifically, first, select an extractant, such as xylene, dichloromethane, chloroform, etc., and then immerse the third composite film in the selected extractant. Adjust the extraction temperature and extraction time to extract some components in the third composite film to form a microporous structure, thereby obtaining the composite lithium-ion battery separator.

[0013] In some embodiments, in step S3, a soft rubber roller is used to roll the inorganic particles so that the inorganic particles are embedded in the substrate film.

[0014] In some embodiments, in step S4, the metal conductivity treatment includes one of electroless plating, physical vapor deposition, or chemical vapor deposition, and the conductive metal in the metal conductivity treatment is one or more of nickel, cobalt, manganese, lithium, and aluminum.

[0015] In some embodiments, step S5, specifically the unidirectional deposition of a nickel metal layer on the second surface of the inorganic particles, involves first depositing a coarse crystal coating on the second surface of the inorganic particles using a high current density, and then depositing a fine crystal coating on the surface of the coarse crystal coating using a low current density, thereby forming a nickel metal layer with a gradient structure composed of the coarse crystal coating and the fine crystal coating.

[0016] 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 a nickel-lithium metal coating deposited faces the positive electrode of the lithium-ion battery, and the side with a nickel metal layer deposited faces the negative electrode of the lithium-ion battery.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: (1) In this invention, an asymmetric metallic conductive coating is constructed on both sides of the composite lithium-ion battery separator. The nickel-lithium coating facing the positive electrode can serve as a "lithium source," slowly releasing lithium ions during cycling to compensate for the irreversible lithium loss caused by the formation of the SEI film on the negative electrode (i.e., "lithium replenishment"). At the same time, this structure helps to stabilize the interface of the positive electrode material and suppress the dissolution of transition metals. The gradient nickel metal layer facing the negative electrode has a fine outer structure that can uniformly distribute the electric field and suppress the growth of lithium dendrites, while the coarse crystalline structure of the inner layer ensures good conductive contact and mechanical support. This bidirectional adjustment function is not available in traditional homogeneous separators.

[0018] (2) The present invention uses the "rolling and embedding" process to firmly anchor inorganic particles in the substrate film, thereby forming a strong "rivet" structure that runs through the separator, which greatly enhances the mechanical strength and puncture resistance of the separator and improves the safety of the battery.

[0019] (3) The present invention avoids the problems of pore blockage and increased interface resistance caused by the use of binders in the traditional coating process by combining rolling embedding and gradient electrodeposition. At the same time, the subsequent extraction pore-forming process also ensures that the membrane has excellent and uniform ion conduction capability.

[0020] (4) The present invention 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. It is particularly suitable for high energy density power batteries and long life energy storage batteries. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of a composite lithium-ion battery separator according to the present invention; Figure 2 This is a flowchart of a method for preparing a composite lithium-ion battery separator according to the present invention; Figure 3 These are cycle performance graphs of the batteries assembled in Example 1 and Comparative Example 1 of this invention after 100 charge-discharge cycles; Figure 4 This is a schematic diagram of the contact angle test of the diaphragms prepared in Example 1 and Comparative Example 1 of the present invention, wherein 4a represents the contact angle result corresponding to the diaphragm prepared in Comparative Example 1, and 4b represents the contact angle result corresponding to the diaphragm prepared in Example 1; Figure 5 These are nitrogen adsorption-desorption isotherm diagrams of the membranes prepared in Example 1 and Comparative Example 1 of this invention, wherein 5a represents the nitrogen adsorption-desorption isotherm of the membrane prepared in Example 1. Figure 5 b represents the nitrogen adsorption-desorption isotherm of the diaphragm prepared in Comparative Example 1.

[0023] In the figure: 1. Substrate film, 2. Inorganic particles, 3. Nickel-lithium metal coating, 4. Nickel metal layer, 41. Coarse crystal coating, 42. Fine crystal coating. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0025] like Figure 1 As shown, the present invention provides a composite lithium-ion battery separator, which includes a substrate film 1 and inorganic particles 2 embedded in the substrate film 1. The two ends of the inorganic particles 2 penetrate the two side surfaces of the substrate film 1, and a nickel-lithium metal coating 3 is compositely deposited on one end surface of the inorganic particles 2, and a nickel metal layer 4 is deposited on the other end surface of the inorganic particles 2. The nickel metal layer 4 is a gradient structure consisting of a coarse crystal plating layer 41 and a fine crystal plating layer 42 deposited sequentially from the surface of the substrate film 1 outward.

[0026] In the above embodiments, the inorganic particles 2 are made of one or more of alumina, silicon dioxide, zirconium oxide or boehmite, and the particle size of the inorganic particles 2 is 1μm-5μm.

[0027] In the above embodiments, the substrate film 1 is made of at least two of polyethylene, polypropylene, polyvinylidene fluoride, or polyimide.

[0028] In the above embodiments, the thickness of the substrate film 1 is 5μm-20μm, the thickness of the nickel-lithium metal coating 3 is 0.05μm-0.5μm, and the total thickness of the nickel metal layer 4 is 0.01μm-1μm, wherein the thickness of the coarse crystal plating layer 41 accounts for at least one-third of the total thickness of the nickel metal layer 4.

[0029] In the above embodiments, the composite lithium-ion battery separator has a microporous structure formed by extraction pore creation, with a porosity of 30%-70%.

[0030] In the above embodiments, asymmetric conductive metal coatings are constructed on both sides of the composite lithium-ion battery separator. Utilizing the different conductive coating structures on both sides, lithium-ion transport can be actively regulated, simultaneously addressing the issues of lithium replenishment at the negative electrode and lithium dissolution at the positive electrode. The nickel-lithium coating facing the positive electrode can act as a "lithium source," slowly releasing lithium ions during cycling to compensate for the irreversible lithium loss caused by the formation of the SEI film at the negative electrode. The gradient nickel metal layer 4 facing the negative electrode has a dense outer structure that provides a uniform electric field distribution, suppressing lithium dendrite growth, while the inner coarse crystalline structure ensures good conductive contact and mechanical support. Therefore, this invention effectively solves the problems of lithium replenishment at the negative electrode and lithium dissolution at the positive electrode, significantly improving the cycle life and capacity retention of lithium-ion batteries.

[0031] like Figure 2 As shown, the present invention also provides a method for preparing a composite lithium-ion battery separator, the method being used to prepare the above-mentioned composite lithium-ion battery separator, comprising the following steps: S1. Mix the selected polymers according to a preset mass ratio and melt blend them at a temperature of 180℃-220℃ to form a composite eutectic matrix; S2. The composite eutectic matrix is ​​extruded or cast to form a substrate film 1; or, the composite eutectic matrix is ​​dissolved in a solvent to prepare a solution, and the solution is cast onto a substrate and dried to form a substrate film 1. S3. Sprinkle inorganic particles 2 of a preset particle size on the surface of the substrate film 1, and roll them to embed the inorganic particles 2 into the substrate film 1, with both ends of the inorganic particles 2 passing through the substrate film 1, to obtain the first composite film. S4. Perform metal conductivity 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 obtain the second composite film. S5. Using the second composite film as the cathode and the insoluble anode as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions, so that a nickel-lithium composite metal coating is unidirectionally deposited on the first surface of the inorganic particle 2. Then, using the second composite film as the cathode and the nickel plate as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions, so that a nickel metal layer 4 is unidirectionally deposited on the second surface of the inorganic particle 2, to obtain a third composite film, wherein the nickel metal layer 4 is a gradient structure composed of a coarse crystal plating layer 41 and a fine crystal plating layer 42 deposited sequentially from the surface outward. S6. Extract and create pores in the third composite film to obtain a composite lithium-ion battery separator.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] To further illustrate the technical principles and effects of the present invention, several specific embodiments and comparative examples are provided below.

[0036] Example 1 (a) The specific steps for preparing the composite lithium-ion battery separator are as follows: 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. 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; 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. 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. S5. Using the second composite film as the cathode and the insoluble anode as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions. First, a nickel-lithium alloy coating with a thickness of 0.2 μm is co-deposited on the alumina particles on one side of the second composite film (the side facing the anode). Then, using the second composite film as the cathode and the nickel plate as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions. 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) 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 structure nickel metal layer 4, 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 gradient structure nickel metal layer 4 are existing technologies and will not be described in detail here. S6. The third composite film is immersed in xylene for extraction to remove some of the soluble polymer components on the third composite film, thereby forming a microporous structure with a porosity of 45%. After drying, the final composite lithium-ion battery separator is obtained.

[0037] (II) Lithium-ion battery assembly Using NCM811 as the positive electrode active material and graphite as the negative electrode active material, positive and negative electrode sheets were prepared according to conventional processes. The prepared composite lithium-ion battery separator was placed between the positive and negative electrode sheets, with the side with the nickel-lithium alloy coating deposited in close contact with the positive electrode sheet and the side with the gradient nickel metal layer 4 deposited in close contact with the negative electrode sheet. A carbonate electrolyte with a conventional lithium salt concentration of 1.0M was injected, and the battery was packaged into a 2032 coin cell.

[0038] Example 2 (a) The specific steps for preparing the composite lithium-ion battery separator are as follows: S1. Mix polyethylene (PE) and polypropylene (PP) with a thickness of 10μm at a mass ratio of 1:1, and stir at 200r / min at 180℃ until the polymers are fully fused to form a composite eutectic matrix. 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; S3. Alumina particles with an average particle size of 1μm 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. 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 0.01 μm on the surface of the first composite film and alumina particles, thereby obtaining the second composite film. S5. Using the second composite film as the cathode and the insoluble anode as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions. First, a nickel-lithium alloy coating with a thickness of 0.05 μm is co-deposited on the alumina particles on one side of the second composite film (the side facing the anode). Then, using the second composite film as the cathode and the nickel plate as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions. A coarse-crystal nickel layer and a fine-crystal 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 structure nickel metal layer 4, thereby obtaining a third composite film, wherein the total thickness of the nickel metal layer 4 is 0.01 μm. S6. The third composite film is immersed in xylene for extraction to remove some of the soluble polymer components on the third composite film, thereby forming a microporous structure with a porosity of 30%. After drying, the final composite lithium-ion battery separator is obtained.

[0039] (II) Lithium-ion battery assembly Using NCM811 as the positive electrode active material and graphite as the negative electrode active material, positive and negative electrode sheets were prepared according to conventional processes. The prepared composite lithium-ion battery separator was placed between the positive and negative electrode sheets, with the side with the nickel-lithium alloy coating deposited in close contact with the positive electrode sheet and the side with the gradient nickel metal layer 4 deposited in close contact with the negative electrode sheet. A carbonate electrolyte with a conventional lithium salt concentration of 1.0M was injected, and the battery was packaged into a 2032 coin cell.

[0040] Example 3 (a) The specific steps for preparing the composite lithium-ion battery separator are as follows: S1. Mix polyethylene (PE) and polypropylene (PP) with a thickness of 20μm at a mass ratio of 3:1, and stir at 220℃ at a speed of 500r / min until the polymers are fully fused to form a composite eutectic matrix. 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; S3. Alumina particles with an average particle size of 5μm 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. 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 0.01 μm on the surface of the first composite film and alumina particles, thereby obtaining the second composite film. S5. Using the second composite film as the cathode and the insoluble anode as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions. First, a nickel-lithium alloy coating with a thickness of 0.5 μm is co-deposited on the alumina particles on one side of the second composite film (the side facing the anode). Then, using the second composite film as the cathode and the nickel plate as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions. A coarse-crystal nickel layer and a fine-crystal 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 structure nickel metal layer 4, thereby obtaining a third composite film, wherein the total thickness of the nickel metal layer 4 is 1 μm. S6. The third composite film is immersed in xylene for extraction to remove some of the soluble polymer components on the third composite film, thereby forming a microporous structure with a porosity of 70%. After drying, the final composite lithium-ion battery separator is obtained.

[0041] (II) Lithium-ion battery assembly Using NCM811 as the positive electrode active material and graphite as the negative electrode active material, positive and negative electrode sheets were prepared according to conventional processes. The prepared composite lithium-ion battery separator was placed between the positive and negative electrode sheets, with the side with the nickel-lithium alloy coating deposited in close contact with the positive electrode sheet and the side with the gradient nickel metal layer 4 deposited in close contact with the negative electrode sheet. A carbonate electrolyte with a conventional lithium salt concentration of 1.0M was injected, and the battery was packaged into a 2032 coin cell.

[0042] Comparative Example 1 Comparative Example 1 was assembled with lithium-ion batteries in the same manner as in Example 1, except that a commercially available separator of the same thickness as the composite lithium-ion battery separator prepared in Example 1 was used.

[0043] Performance testing (1) The batteries assembled in Example 1 and Comparative Example 1 were subjected to charge-discharge cycle tests under the same conditions, with 100 tests conducted. Figure 3 As shown, Figure 3 Center line ① shows the cycle performance results of the battery assembled in Example 1 after 100 charge-discharge cycles. Figure 3 Center line ② shows the cycle performance results of the battery assembled in Comparative Example 1 after 100 charge-discharge cycles. Figure 3 As can be seen, after 100 charge-discharge cycles, the capacity of Comparative Example 1 decreased significantly, while the capacity of the battery assembled with the composite lithium-ion battery separator provided by the present invention (Example 1) remained above 96% after 100 charge-discharge cycles. This is because the composite lithium-ion battery separator provided by the present invention has lithium replenishment and nickel layer suppression effects, thereby significantly improving the capacity retention rate and cycle life of the lithium-ion battery.

[0044] (2) The separators prepared in Example 1 and Comparative Example 1 were used as battery separators and mixed with positive electrode active material LiCoO2, conductive agent and binder PVDF in a mass ratio of 8:1:1 to form a slurry. The slurry was then uniformly coated onto aluminum foil with a medical scraper, air-dried, and then formed into round sheets (12 mm in diameter). The sheets were then vacuum dried at 105 °C (133 Pa) for 10 h to obtain electrode sheets (active material content 3 mg). Using lithium metal sheets as negative electrodes and 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1) as electrolyte, CR2032 coin cells were assembled in an argon-filled glove box. The contact angle was then tested at 25 °C with a test voltage of 2.0-4.5 V. The test results are as follows. Figure 4 As shown, Figure 4 a shows the contact angle results corresponding to the diaphragm prepared in Comparative Example 1. Figure 4 b shows the contact angle results corresponding to the diaphragm prepared in Example 1, from... Figure 4 As can be seen, the contact angle of the separator prepared in Example 1 is significantly larger than that in Comparative Example 1. A larger contact angle indicates better wettability, meaning that the separator prepared in Example 1 has better electrolytic wettability. When a separator with good electrolytic wettability comes into contact with the electrolyte, the good electrolyte wettability ensures thorough electrolyte wetting and increases the retention time of the electrolyte in the separator. Therefore, the separator prepared in Example 1 is beneficial for increasing the cycle life of the battery.

[0045] (3) The membranes prepared in Example 1 and Comparative Example 1 were subjected to nitrogen adsorption-desorption tests. The test results are as follows: Figure 5 As shown, Figure 5 a shows the nitrogen adsorption-desorption isotherm of the diaphragm prepared in Example 1. Figure 5 b shows the nitrogen adsorption-desorption isotherm of the membrane prepared in Comparative Example 1, from... Figure 5 As 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 -1Therefore, 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.

[0046] (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.

[0047] Table 1. Charge-discharge cycle test results of batteries assembled in Examples 1-3 and Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 1 Battery capacity retention rate (%) after 500 cycles 95 94 92 76 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.

[0048] 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 in that, The invention includes a substrate film and inorganic particles embedded in the substrate film. The two ends of the inorganic particles penetrate the two sides of the substrate film. One end of the inorganic particles is coated with a nickel-lithium metal coating, and the other end of the inorganic particles is coated with a nickel metal layer. The nickel metal layer is a gradient structure consisting of a coarse crystal coating and a fine crystal coating deposited sequentially from the surface of the substrate film.

2. The composite lithium-ion battery separator according to claim 1, characterized in that, The inorganic particles are made of one or more of alumina, silicon dioxide, zirconium oxide, or boehmite, and the particle size of the inorganic particles is 1μm-5μm.

3. The composite lithium-ion battery separator according to claim 1, characterized in that, The substrate film is made of at least two of polyethylene, polypropylene, polyvinylidene fluoride, or polyimide.

4. The composite lithium-ion battery separator according to claim 1, characterized in that, The thickness of the substrate film is 5μm-20μm, the thickness of the nickel-lithium metal coating is 0.05μm-0.5μm, and the total thickness of the nickel metal layer is 0.01μm-1μm, wherein the thickness of the coarse crystal coating accounts for at least one-third of the total thickness of the nickel metal layer.

5. The composite lithium-ion battery separator according to claim 1, characterized in that, The composite lithium-ion battery separator has a microporous structure formed by extraction pore creation, with a porosity of 30%-70%.

6. A method for preparing a composite lithium-ion battery separator, characterized in that, The method is used to prepare the composite lithium-ion battery separator as described in any one of claims 1 to 5, and includes the following steps: S1. Mix the selected polymers according to a preset mass ratio and melt blend them at a temperature of 180℃-220℃ to form a composite eutectic matrix; S2. The composite eutectic matrix is ​​extruded or cast to form a substrate film; or, the composite eutectic matrix is ​​dissolved in a solvent to prepare a solution, and the solution is cast onto a substrate and dried to form a substrate film. S3. Inorganic particles of a preset particle size are sprayed onto the surface of the substrate film by spraying. The inorganic particles are then embedded into the substrate film by rolling, with both ends of the inorganic particles penetrating the substrate film to obtain the first composite film. S4. Perform metal conductivity treatment on the first composite film to form a metal conductive layer on the surface of the first composite film and the inorganic particles, thereby obtaining the second composite film. S5. Using the second composite film as the cathode and the insoluble anode as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions and lithium ions, so that a nickel-lithium composite metal coating is unidirectionally deposited on the first surface of the inorganic particles. Then, using the second composite film as the cathode and the nickel plate as the anode, unidirectional electrochemical deposition is performed in an electrolyte containing nickel ions, so that a nickel metal layer is unidirectionally deposited on the second surface of the inorganic particles, to obtain a third composite film, wherein the nickel metal layer is a gradient structure consisting of a coarse crystal coating and a fine crystal coating deposited sequentially from the surface outward. S6. Extract and create pores in 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 so that the inorganic particles are embedded into the substrate film.

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

9. The preparation method according to claim 6, characterized in that, In step S5, the unidirectional deposition of a nickel metal layer on the second surface of the inorganic particles specifically involves: first depositing a coarse crystal coating on the second surface of the inorganic particles using a high current density, and then depositing a fine crystal coating on the surface of the coarse crystal coating using a low current density, thereby forming a nickel metal layer with a gradient structure composed of the coarse crystal coating and the fine crystal coating.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes 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 according to any one of claims 1 to 5 or the composite lithium-ion battery separator prepared by the preparation method according to any one of claims 6 to 9. The side of the composite lithium-ion battery separator with the nickel-lithium metal coating deposited faces the positive electrode of the lithium-ion battery, and the side with the nickel metal layer deposited faces the negative electrode of the lithium-ion battery.

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