A multistage gradient biomimetic coupling composite diaphragm and a preparation method thereof

Abstract

The application discloses a multistage gradient biomimetic coupling composite diaphragm and a preparation method thereof, and relates to the technical field of lithium battery diaphragms. The composite diaphragm comprises a biomimetic interwoven composite fiber matrix, a multistage gradient microporous structure and double-sided atomic-level modification coatings; the multistage gradient micropores are arranged in layers along the thickness and are adapted to the multistage gradient biomimetic composite positive and negative electrodes in a mirror image mode; the biomimetic interwoven matrix improves the mechanical stability, and the double-sided ALD coatings are respectively adapted to the positive and negative electrode interfaces to inhibit side reactions and lithium dendrite growth. The application solves the technical problems of poor matching, high interface impedance and insufficient mechanical stability of the existing diaphragm homogeneous structure, is suitable for multiple types of lithium battery systems, improves the fast charging capability, safety and reliability and cycle life of the battery, and has extremely high industrialization and patent application value.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, specifically to a multi-level gradient biomimetic coupling composite separator and its preparation method, applicable to liquid lithium batteries, semi-solid lithium batteries and all-solid lithium batteries. Background Technology

[0002] As the isolation and ion transport medium between the positive and negative electrodes, lithium battery separators must possess insulation, microporous conductivity, mechanical stability, and interface compatibility. Existing commercial separators are mostly homogeneous microporous structures, primarily made of polypropylene (PP) and polyethylene (PE), which have the following technical drawbacks: First, the homogeneous pore size design cannot match the differences in ion transport rates at the electrode interfaces, resulting in high interface impedance and severe concentration polarization, limiting the battery's fast-charging performance. Second, conventional separators lack sufficient mechanical strength, exhibiting weak vibration and puncture resistance, making them prone to damage under extreme conditions, inducing micro-short circuits and thermal runaway risks. Third, the poor compatibility between the separator and electrode interfaces makes side reactions more likely, leading to accelerated capacity decay during cycling. Fourth, a single structural design is difficult to adapt to the ion transport characteristics of multi-level gradient composite electrodes, resulting in insufficient system compatibility. Currently, a limited number of gradient separator studies focus only on adjusting the pore size in a single dimension, without combining it with the electrode gradient structure for mirror matching, or introducing biomimetic interwoven frameworks and atomic-level interface modification. This makes it impossible to achieve synergistic optimization from multiple dimensions of structure, mechanics, and interface, resulting in poor industrial adaptability and difficulty in meeting the application requirements of high-safety, high-rate, and long-life lithium batteries. Summary of the Invention

[0003] Technical issues To address the shortcomings of existing technologies, this invention provides a multi-level gradient biomimetic coupling composite separator and its preparation method, solving the technical problems of poor homogeneous structure matching, high interface impedance, insufficient mechanical stability, weak anti-dendrying ability, poor cycle stability, and easy circumvention by existing technologies. It is adapted to multi-level gradient biomimetic composite positive and negative electrode structures, improving battery fast charging performance, safety, reliability, and cycle life. Technical solution A multi-level gradient biomimetic coupling composite diaphragm The composite membrane comprises a biomimetic interwoven composite fiber matrix, a multi-level gradient microporous structure, and a double-sided atomic-level modified coating; The biomimetic interwoven composite fiber matrix uses PVDF-HFP / PI composite nanofibers, which form a continuous interconnected topological structure through disordered three-dimensional biomimetic interweaving. After a single fiber breaks locally, it is constrained by the surrounding interwoven fibers, and no free debris is generated. The diameter of the composite fiber is controlled at 200nm–1μm, the overall Young's modulus of the matrix is ​​≥20GPa, the breaking elongation is ≥10%, and it can withstand 5–15g vibration and impact conditions. The multi-level gradient microporous structure is arranged in layers along the thickness direction of the membrane, which is adapted to the multi-level gradient biomimetic composite positive and negative electrode structure: the macroporous layer is near the positive electrode, with a pore size of 300–800 nm and a porosity of 65%–75%; the middle layer is a mesoporous transition layer with a pore size of 50–200 nm and a porosity of 60%–70%; the microporous layer is near the negative electrode, with a pore size of 10–50 nm and a porosity of 55%–65%; the overall pore connectivity is ≥90%, realizing ion gradient transport and smooth transition of interface impedance; The dual-sided atomic-level modified coatings are coated on both sides of the separator substrate using atomic layer deposition (ALD) technology. The positive electrode side is a high-voltage stable ceramic coating, made of either alumina or zirconium oxide, with a coating thickness of 3–10 nm. It is continuous, dense, and free of pinholes, and can withstand a high-voltage, strong-oxidation environment of 4.2 V–4.8 V. The negative electrode side is a lithiophilic induction coating, made of either graphene quantum dots or lithium-based composite oxides, with a coating thickness of 3–10 nm. It provides uniform coverage without any gaps in the coating, guides the uniform deposition of lithium ions, and inhibits the growth of lithium dendrites. A method for preparing a multi-level gradient biomimetic coupled composite diaphragm Raw material pretreatment: PVDF-HFP / PI composite fiber raw materials are added to a polar dispersant and then subjected to ultrasonic dispersion and low-temperature plasma surface activation treatment to remove fiber agglomerates and surface impurities, thereby improving the film-forming properties and interweaving stability of the fiber surface; Multi-level gradient microporous matrix forming: Using an electrospinning combined with layer-by-layer deposition process, a macroporous layer near the positive electrode, an intermediate mesoporous transition layer, and a microporous layer near the negative electrode are prepared sequentially according to the pore size from large to small, to obtain a multi-level gradient biomimetic interwoven membrane preform; the electrospinning voltage is 12–18 kV, the receiving distance is 15–25 cm, and the solution concentration is 8–15 wt%; Heat setting and curing: The diaphragm blank is placed in an inert atmosphere for segmented heat setting treatment. The first segment temperature is 80–120℃ and the holding temperature is 30–60 min. The second segment temperature is 150–180℃ and the holding temperature is 20–40 min to eliminate internal stress and improve the mechanical stability of the matrix. Double-sided atomic layer deposition modification: Using atomic layer deposition process, a high-pressure stable ceramic coating is first deposited on the positive electrode side surface of the separator, and then the separator is flipped to deposit a lithium-inducible coating on the negative electrode side surface; the deposition temperature is 100–250℃, the deposition cycle is 10–50 cycles, and the coating thickness is precisely controlled to 3–10nm with a thickness control accuracy of ±0.5nm. Defect correction and cutting: The modified diaphragm is subjected to surface defect detection and slight cross-linking strengthening treatment to repair micro-pore defects. Then it is cut according to specifications to obtain the multi-level gradient biomimetic coupling composite diaphragm product. Beneficial effects Employing a multi-level gradient microporous structure, mirror-matched with a multi-level gradient biomimetic composite positive and negative electrode, it achieves smooth transition of ion gradient transport and interface impedance, significantly reduces concentration polarization, and significantly improves battery fast charging performance. The biomimetic interwoven composite fiber matrix has excellent mechanical properties. Local fractures do not produce free debris, effectively adapting to extreme vibration and impact conditions such as vehicle and energy storage, and eliminating the risk of micro-short circuits caused by debris from the root. The dual-sided atomic-level modified coatings are adapted to the positive and negative electrode interfaces respectively. The ceramic coating on the positive electrode side is resistant to high pressure and strong oxidation environment and suppresses the occurrence of side reactions. The lithium-loving coating on the negative electrode side guides the uniform deposition of lithium ions, effectively suppresses the growth of lithium dendrites, and improves the safety and reliability of the battery. The structural design is compatible with liquid, semi-solid and all-solid lithium battery systems, and when used with multi-level gradient biomimetic composite positive and negative electrodes, it can achieve synergistic improvement in battery performance. The preparation process adopts mature electrospinning, heat setting and atomic layer deposition technologies. The process is controllable, adaptable to existing mass production lines, and the products have high consistency and have extremely high industrial application value.

Claims

1. A multi-level gradient biomimetic coupling composite diaphragm, characterized in that, The structure comprises a biomimetic interwoven composite fiber matrix, a multi-level gradient microporous structure, and a double-sided atomic-level modified coating. The biomimetic interwoven composite fiber matrix is ​​a three-dimensional interconnected topology of PVDF-HFP / PI composite nanofibers with a fiber diameter of 200 nm–1 μm, an overall Young's modulus ≥20 GPa, and a breaking elongation ≥10%. The multi-level gradient microporous structure is divided into three layers along the thickness direction: a macroporous layer with a pore size of 300–800 nm and a porosity of 65%–75% near the positive electrode; a mesoporous transition layer with a pore size of 50–200 nm and a porosity of 60%–70%; and a microporous layer with a pore size of 10–50 nm and a porosity of 55%–65% near the negative electrode. The double-sided atomic-level modified coating is an ALD deposition layer, with an alumina / zirconia coating on the positive electrode side and a graphene quantum dot / lithium-based composite oxide coating on the negative electrode side, with a coating thickness of 3–10 nm.

2. The multi-level gradient biomimetic coupling composite diaphragm according to claim 1, characterized in that, The overall pore connectivity of the multi-level gradient microporous structure is ≥90%.

3. The multi-level gradient biomimetic coupling composite diaphragm according to claim 1, characterized in that, The atomically modified coating on the positive electrode side is resistant to a high-voltage, strong-oxidation environment of 4.2V–4.8V.

4. The multi-level gradient biomimetic coupling composite diaphragm according to claim 1, characterized in that, The composite separator is compatible with liquid lithium batteries, semi-solid lithium batteries and all-solid lithium battery systems.

5. A method for preparing a multi-level gradient biomimetic coupled composite diaphragm, characterized in that, Includes the following steps: (1) The PVDF-HFP / PI composite fiber raw material was pretreated by ultrasonic dispersion and low temperature plasma activation to obtain a uniformly dispersed fiber raw material; (2) Using electrospinning combined with layer-by-layer deposition process, macroporous layer, mesoporous transition layer and microporous layer are prepared in sequence to obtain multi-level gradient biomimetic interwoven membrane preform; (3) Segmented heat setting and curing under an inert atmosphere to eliminate internal stress; (4) A high-voltage stabilizing ceramic coating on the positive electrode side and a lithium-inducing coating on the negative electrode side are deposited on both sides of the separator by atomic layer deposition process; (5) Defects are repaired and cut to obtain the composite diaphragm product.

6. The preparation method according to claim 5, characterized in that, The electrospinning process parameters are: voltage 12–18kV, receiving distance 15–25cm, and solution concentration 8–15wt%.

7. The preparation method according to claim 5, characterized in that, The segmented heat setting process is as follows: the first segment is held at 80–120℃ for 30–60 minutes, and the second segment is held at 150–180℃ for 20–40 minutes.

8. The preparation method according to claim 5, characterized in that, Atomic layer deposition temperature 100–250℃, deposition cycle 10–50 cycles, coating thickness control accuracy ±0.5nm.