Gradient thermal response composite nanofiber diaphragm and preparation method thereof

Abstract

The invention discloses a gradient thermal response composite nanofiber diaphragm and a preparation method thereof. The composite nanofiber diaphragm is composed of three functional layers: a) a surface layer: a low-density polyimide nanofiber layer (porosity is 60%-80%), and doped nano zirconium dioxide (5-10 wt%) improves the wettability of an electrolyte; b) a middle layer: polyimide / boron nitride nanosheet composite fibers (the content of boron nitride is 15-20wt%) form a three-dimensional heat conduction network; c) a bottom layer: a thermally induced phase change layer (polyimide and phase change microcapsule co-spinning) which triggers a hole closing effect at 160 DEG C; an in-situ electrostatic spinning composite process: adopting a coaxial nozzle for synchronous spinning; injecting a polyimide spinning solution containing boron nitride into an inner layer, and injecting a phase change microcapsule suspension into an outer layer; and an electric field gradient control technology (the voltage is gradually reduced from 25kV to 18kV) is introduced, so that the gradient distribution of the fiber diameter from 80nm to 200nm is realized. Through the innovative structural design and the advanced preparation process, the safety, the performance and the reliability of the lithium ion battery under the high-temperature working condition are remarkably improved, and important technical support is provided for the development of the high-performance lithium ion battery. The 180 DEG C thermal shrinkage rate of the product is less than 2% (reduced by more than 40% compared with the prior art); and the bottom layer closed hole response time during thermal runaway is less than 8 seconds (the traditional diaphragm is more than 15 seconds).

Description

Technical Field

[0001] The present invention relates to a composite nanofiber diaphragm with a gradient thermal response prepared by an electrospinning-in-situ composite technology, which is suitable for the safety protection of lithium-ion batteries under high-temperature working conditions. Background Art

[0002] With the rapid development of new energy technologies, lithium-ion batteries, as efficient and environmentally friendly energy storage devices, are widely used in electric vehicles, portable electronic devices, energy storage systems, and other fields. Their high energy density, long cycle life, and relatively low self-discharge rate make them an ideal energy storage solution. However, with the continuous expansion of application scenarios, especially in areas such as electric vehicles and energy storage systems that require extremely high battery safety, the safety of lithium-ion batteries under high-temperature conditions is gaining increasing attention.

[0003] Traditional polyolefin separators (such as polyethylene and polypropylene) are prone to thermal shrinkage at high temperatures. Traditional separators mainly rely on their own thermal stability to prevent battery short circuits at high temperatures. They lack active thermal protection mechanisms and are unable to promptly block heat transfer when the temperature inside the battery rises abnormally. In other words, existing lithium-ion battery separators still have problems such as insufficient thermal stability, poor electrolyte wettability, and lack of active protection functions under high-temperature conditions. They are difficult to meet the needs of application scenarios such as electric vehicles and energy storage systems that have extremely high battery safety requirements. Therefore, the development of a new high-temperature separator with excellent thermal stability, good electrolyte wettability, and active thermal protection functions is of great significance for improving the safety and reliability of lithium-ion batteries. Summary of the Invention

[0004] The present invention proposes to provide a gradient thermal response composite nanofiber membrane and a preparation method thereof. The membrane achieves excellent performance under high temperature conditions through a unique gradient thermal response structure design and in-situ electrospinning composite process, which can effectively improve the safety and stability of lithium-ion batteries.

[0005] The technical solution of the present invention is achieved as follows:

[0006] A gradient thermal response composite nanofiber membrane, characterized by comprising a three-layer composite structure:

[0007] a) Surface layer: A porous layer composed of low-density polyimide nanofibers with a porosity of 60%-80%, in which 5%-10% by mass of nano-zirconium dioxide particles are uniformly dispersed;

[0008] b) Intermediate layer: a three-dimensional thermal conductive network layer composed of a polyimide matrix and 15%-20% by mass of boron nitride nanosheets;

[0009] c) Bottom layer: a closed-cell functional layer formed by co-spinning polyimide and thermally induced phase-change microcapsules. The phase-change microcapsules trigger the closed-cell effect at 160°C.

[0010] Preferably, the fiber diameter of the separator is distributed in a gradient from the surface layer to the bottom layer, and the fiber diameter ranges from 80 nm to 200 nm.

[0011] Preferably, the thermal shrinkage of the separator at 180° C. is less than 2%.

[0012] Preferably, the phase change temperature of the phase change microcapsules is 160°C±5°C.

[0013] A method for preparing a gradient thermal responsive composite nanofiber membrane, the process comprising the following steps:

[0014] a) preparing a polyimide spinning solution, wherein the solution is doped with 5-10 wt % of nano zirconium dioxide;

[0015] b) preparing a polyimide spinning solution containing boron nitride, wherein the boron nitride content in the solution is 15-20 wt %;

[0016] c) preparing a phase change microcapsule suspension;

[0017] d) electrospinning using a coaxial nozzle, injecting a polyimide spinning solution containing boron nitride into the inner layer and a phase change microcapsule suspension into the outer layer;

[0018] e) Introducing electric field gradient control technology during the spinning process, gradually reducing the voltage from 25kV to 18kV to achieve a gradient distribution of fiber diameter from 80nm to 200nm;

[0019] f) collecting the composite nanofibers obtained by spinning to form a diaphragm with a gradient thermal response structure.

[0020] Compared with the existing technology, the beneficial effects or advantages of the present invention are mainly reflected in the following aspects: through innovative structural design and advanced preparation technology, the safety, performance and reliability of lithium-ion batteries under high-temperature conditions are significantly improved, providing important technical support for the development of high-performance lithium-ion batteries.

[0021] The product's 180°C thermal shrinkage is less than 2% (reduced by more than 40% compared to existing technologies); the bottom layer closed cell response time during thermal runaway is less than 8 seconds (traditional diaphragms are greater than 15 seconds). DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0023] Example

[0024] This embodiment provides a gradient thermal response composite nanofiber membrane, comprising a three-layer composite structure:

[0025] a) Surface layer: A porous layer composed of low-density polyimide nanofibers with a porosity of 60%-80%, in which 5%-10% by mass of nano-zirconium dioxide particles are uniformly dispersed;

[0026] b) Intermediate layer: a three-dimensional thermal conductive network layer composed of a polyimide matrix and 15%-20% by mass of boron nitride nanosheets;

[0027] c) Bottom layer: a closed-cell functional layer formed by co-spinning polyimide and thermally induced phase-change microcapsules. The phase-change microcapsules trigger the closed-cell effect at 160°C.

[0028] Preferably, the fiber diameter of the separator is distributed in a gradient from the surface layer to the bottom layer, and the fiber diameter ranges from 80 nm to 200 nm.

[0029] Preferably, the thermal shrinkage of the separator at 180° C. is less than 2%.

[0030] Preferably, the phase change temperature of the phase change microcapsules is 160°C±5°C.

[0031] A method for preparing a gradient thermal responsive composite nanofiber membrane, the process comprising the following steps:

[0032] a) preparing a polyimide spinning solution, wherein the solution is doped with 5-10 wt % of nano zirconium dioxide;

[0033] b) preparing a polyimide spinning solution containing boron nitride, wherein the boron nitride content in the solution is 15-20 wt %;

[0034] c) preparing a phase change microcapsule suspension;

[0035] d) electrospinning using a coaxial nozzle, injecting a polyimide spinning solution containing boron nitride into the inner layer and a phase change microcapsule suspension into the outer layer;

[0036] e) Introducing electric field gradient control technology during the spinning process, gradually reducing the voltage from 25kV to 18kV to achieve a gradient distribution of fiber diameter from 80nm to 200nm;

[0037] f) collecting the composite nanofibers obtained by spinning to form a diaphragm with a gradient thermal response structure.

[0038] The present invention is further described:

[0039] 1. The role of the diaphragm

[0040] (1) Improving the high-temperature safety of lithium-ion batteries

[0041] 1. Thermal runaway protection: During the operation of lithium-ion batteries, especially under high-temperature conditions, thermal runaway is easily caused by heat accumulation inside the battery. The bottom layer of the diaphragm of the present invention adopts a closed-cell functional layer formed by co-spinning of thermo-induced phase change microcapsules and polyimide. When the temperature reaches 160°C, the phase change microcapsules quickly trigger the closed-cell effect, which can effectively block the heat transfer and chemical reactions inside the battery and prevent the further spread of thermal runaway. Compared with traditional diaphragms, the closed-cell response time is shortened to less than 8 seconds, while traditional diaphragms usually require more than 15 seconds, which significantly improves the safety of the battery at high temperatures.

[0042] 2. Low thermal shrinkage: The separator's thermal shrinkage at 180°C is less than 2%, which is over 40% lower than existing technologies. This feature enables the separator to maintain a stable structure in high-temperature environments, preventing internal battery short circuits caused by separator shrinkage, further reducing the risk of battery fire and explosion.

[0043] (2) Optimizing battery performance

[0044] 1. Enhanced electrolyte wettability: The surface layer of the separator is composed of low-density polyimide nanofibers with a porosity of 60%-80%, doped with 5%-10% nano-zirconium dioxide particles. This design significantly improves electrolyte wettability, allowing the electrolyte to be more evenly distributed on the separator surface, thereby improving the battery's ion transport efficiency and enhancing the battery's charge and discharge performance.

[0045] 2. Efficient Thermal Conductivity: The middle layer is composed of a polyimide matrix and 15%-20% boron nitride nanosheets, forming a three-dimensional thermal network. The boron nitride nanosheets have excellent thermal conductivity, rapidly conducting heat generated within the battery. This allows the battery to maintain good thermal management even under high-temperature conditions, preventing local overheating from affecting battery performance and extending its lifespan.

[0046] (3) Adapting to high temperature environment

[0047] The membrane's gradient thermal response structure enables it to maintain stable performance in high-temperature environments, making it suitable for lithium-ion battery applications such as electric vehicles and energy storage systems that require high-temperature operation. This membrane meets the stringent requirements for high-temperature safety and stability in these applications, ensuring reliable battery operation under extreme operating conditions.

[0048] 2. The role of preparation method

[0049] (1) Achieving precise construction of gradient structures

[0050] 1. Coaxial Spinning: Electrospinning is performed using a coaxial nozzle. A polyimide spinning solution containing boron nitride is injected into the inner layer, while a phase-change microcapsule suspension is injected into the outer layer. This synchronous spinning technology forms the middle and bottom layers simultaneously in a single spinning process, ensuring a tight bond between the layers and avoiding the interlayer separation issues that can occur with traditional multilayer composite processes.

[0051] 2. Electric Field Gradient Control: Introducing electric field gradient control technology during the spinning process, gradually reducing the voltage from 25kV to 18kV, allows precise control of the fiber diameter distribution, gradually transitioning from 80nm at the surface to 200nm at the bottom, creating a gradient fiber structure. This gradient structure not only helps achieve the membrane's gradient thermal response function, but also optimizes the membrane's mechanical properties and ion transport performance.

[0052] (2) Improve production efficiency and quality

[0053] 1. Integrated molding: The three-layer structure of the entire diaphragm can be formed through a single electrospinning process, which simplifies the production process, reduces production steps, improves production efficiency, and reduces production costs.

[0054] 2. Uniform dispersion and uniform compounding: This process can ensure the uniform dispersion of nano-zirconium dioxide particles on the surface layer and the uniform distribution of boron nitride nanosheets in the middle layer, thereby ensuring the stable function of each layer of the diaphragm and improving the uniformity and consistency of product quality.

[0055] (3) Scalability and flexibility

[0056] This preparation method has good scalability. According to different battery requirements, by adjusting the composition of the spinning solution, electric field parameters and other conditions, gradient thermal response composite nanofiber membranes with different performance indicators can be flexibly prepared to meet diverse market needs.

[0057] The following is an example of a "polyimide / ceramic nanofiber high-temperature lithium battery separator based on a gradient composite structure and a preparation method thereof":

[0058] 1. Raw material preparation (refer to above)

[0059] 2. Spinning process

[0060] 1. Start the device:

[0061] The surface spinning solution was loaded into the syringe pump and the flow rate was adjusted to 0.5 mL / h.

[0062] The intermediate layer spinning solution and the phase change microcapsule suspension were respectively loaded into the inner layer and outer layer of the coaxial nozzle, and the flow rates were adjusted to 0.8 mL / h and 0.3 mL / h, respectively.

[0063] 2. Spinning operation:

[0064] The power supply was turned on, the initial voltage was set to 25 kV, and spinning began.

[0065] During the spinning process, the voltage was gradually reduced to 18 kV to achieve a gradient distribution of fiber diameter from 80 nm to 200 nm.

[0066] Maintaining stable environmental conditions during the spinning process ensures uniform fiber formation.

[0067] 3. Collecting Fiber:

[0068] After spinning is completed, the formed composite nanofiber membrane is peeled off from the collecting device.

[0069] 3. Post-processing

[0070] (1) Drying treatment

[0071] 1. Dry the composite nanofiber membrane obtained by spinning at 60°C for 12 hours to remove residual solvent and ensure the structural stability of the membrane.

[0072] (2) Performance test

[0073] 1. Thermal shrinkage test:

[0074] The separator sample was placed in an oven at 180°C for 1 hour, and its dimensional change was measured.

[0075] The test results show that the thermal shrinkage rate of the diaphragm is less than 2%, which meets the design requirements.

[0076] 2. Closed cell response time test:

[0077] The diaphragm samples were placed in a thermal environment at 160°C to observe the triggering time of the closed-cell effect of the underlying layer.

[0078] The test results show that the closed-cell response time is less than 8 seconds, which is significantly better than the traditional diaphragm (the closed-cell response time of the traditional diaphragm is greater than 15 seconds).

[0079] The above-mentioned preparation process successfully fabricated a polyimide / ceramic nanofiber separator with a gradient thermal response structure. This separator exhibits excellent thermal stability and rapid cell closure response under high-temperature conditions, effectively improving the safety of lithium-ion batteries. The gradient distribution of fiber diameter further optimizes the separator's mechanical and ion transport properties, giving it broad application prospects in practical applications.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gradient thermal response composite nanofiber membrane, characterized by: Contains three-layer composite structure: a) Surface layer: A porous layer composed of low-density polyimide nanofibers with a porosity of 60%-80%, in which 5%-10% by mass of nano-zirconium dioxide particles are uniformly dispersed; b) Intermediate layer: a three-dimensional thermal conductive network layer composed of a polyimide matrix and 15%-20% by mass of boron nitride nanosheets; c) Bottom layer: a closed-cell functional layer formed by co-spinning polyimide and thermally induced phase-change microcapsules. The phase-change microcapsules trigger the closed-cell effect at 160°C.

2. The gradient thermal response composite nanofiber membrane according to claim 1, characterized in that: The fiber diameter of the separator is distributed in a gradient from the surface layer to the bottom layer, and the fiber diameter ranges from 80 nm to 200 nm.

3. The gradient thermal response composite nanofiber membrane according to claim 1, characterized in that: The thermal shrinkage rate of the separator at 180° C. is less than 2%.

4. The gradient thermal response composite nanofiber membrane according to claim 1, characterized in that: The phase change temperature of the phase change microcapsule is 160°C±5°C.

5. A method for preparing a gradient thermally responsive composite nanofiber membrane, characterized by: A gradient thermal responsive composite nanofiber membrane according to any one of claims 1 to 4 is used, comprising an in-situ electrospinning composite process, the process comprising the following steps: a) preparing a polyimide spinning solution, wherein the solution is doped with 5-10 wt % of nano zirconium dioxide; b) preparing a polyimide spinning solution containing boron nitride, wherein the boron nitride content in the solution is 15-20 wt %; c) preparing a phase change microcapsule suspension; d) electrospinning using a coaxial nozzle, injecting a polyimide spinning solution containing boron nitride into the inner layer and a phase change microcapsule suspension into the outer layer; e) Introducing electric field gradient control technology during the spinning process, gradually reducing the voltage from 25kV to 18kV to achieve a gradient distribution of fiber diameter from 80nm to 200nm; f) collecting the composite nanofibers obtained by spinning to form a diaphragm with a gradient thermal response structure.