Thermally conductive phase change materials, their preparation methods and applications

Abstract

This invention relates to the field of battery materials, specifically to a thermally conductive phase change material, its preparation method, and its applications. The thermally conductive phase change material provided by this invention has a core-shell structure, comprising a ceramic material as the core and a shell layer covering the surface of the core. The shell layer contains a thermosensitive agent and a thermally conductive agent, with a mass ratio of the thermosensitive agent to the thermally conductive agent of (1-50):1, and a mass ratio of the core to the shell layer of (8-500):1. The thermally conductive phase change material provided by this invention has high thermal conductivity and can rapidly undergo a melting phase change upon heating, interrupting the ion transport process in the ion-based battery system, effectively avoiding and preventing battery thermal runaway, and improving battery safety.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a thermally conductive phase change material, its preparation method, and its application. Background Technology

[0002] The increasing consumption and demand for fossil fuels has led to environmental pollution and energy crises, seriously threatening human survival and development. Vigorously developing and utilizing renewable and clean energy sources such as solar, wind, and hydropower can effectively reduce dependence on fossil fuels and environmental pollution. However, the inherent volatility and immediacy of renewable energy sources limit their widespread application. Developing efficient energy storage technologies can promote the development of the renewable energy technology market and ensure national energy security.

[0003] Lithium iron phosphate (LFP) batteries boast numerous advantages, including long lifespan, fast start-up, safety, high efficiency, and low cost, making them widely applicable in electrochemical energy storage power stations, electric vehicles, and drones. They have become the fastest-growing and most technologically mature lithium-ion battery technology. However, one of the biggest challenges of LFP batteries is the poor thermal stability of their polyolefin separators. Under conditions of mechanical, electrical, and thermal abuse, the separator is prone to rupture, shrinkage, softening, and even melting, leading to internal short circuits and triggering thermal runaway.

[0004] Currently, a common approach is to coat the membrane surface with rigid microspheres coated with heat-sensitive agents to achieve thermal stability and heat-sensitive self-sealing properties. However, the heat-sensitive agents on the surface of rigid microspheres are mostly polymers such as polyethylene, which have low thermal conductivity (the thermal conductivity of polyethylene is 0.39 W / m²). -1 K -1 High latent heat of phase change (the latent heat of phase change of polyethylene is 210 J / g). -1 It has a long thermal response time, making it difficult to quickly melt and seal ion transport channels. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor thermal stability, low thermal conductivity, and long thermal response time of coating materials used in battery separators in the prior art, thereby providing a thermally conductive phase change material that can effectively prevent and stop battery thermal runaway.

[0006] To achieve the above objectives, the first aspect of the present invention provides a thermally conductive phase change material, wherein the thermally conductive phase change material has a core-shell structure, comprising a ceramic material as the core and a shell layer covering the surface of the core, the shell layer comprising a thermosensitive agent and a thermally conductive agent, wherein the mass ratio of the thermosensitive agent to the thermally conductive agent is (1-50):1, and the mass ratio of the core to the shell layer is (8-500):1.

[0007] Preferably, the ceramic material is at least one of boehmite and alumina ceramic;

[0008] Preferably, the heat sensitizer is at least one of polyethylene, thermoplastic polyurethane rubber, and ethylene-vinyl acetate copolymer.

[0009] Preferably, the thermal conductive agent is at least one selected from diamond, graphite, carbon powder, graphene, carbon nanotubes, aluminum nitride, aluminum oxide, boron nitride, and zinc oxide.

[0010] Preferably, the thermal conductive agent is a composition of carbon powder, alumina and boron nitride in a mass ratio of 1:(0.3-0.8):(0.1-0.5).

[0011] Preferably, the thermally conductive phase change material is a thermally conductive phase change microsphere, the average particle size of the thermally conductive phase change microsphere is 1000nm-5000nm, and the average thickness of the shell is 100nm-1000nm.

[0012] A second aspect of the present invention provides a method for preparing the thermally conductive phase change material provided in the first aspect, comprising the following steps:

[0013] The thermally conductive phase change material is obtained by coating a shell containing a heat-sensitive agent and a thermally conductive agent onto the surface of a ceramic material that serves as the core using a solution coating method or a melt phase change coating method.

[0014] In the shell layer, the mass ratio of the heat sensitizer to the thermally conductive agent is (1-50):1; in the thermally conductive phase change material, the mass ratio of the core to the shell layer is (8-500):1.

[0015] Preferably, the solution coating method includes the following steps: mixing the heat sensitizer and the thermally conductive agent in an organic solvent to obtain a mixture; adding the ceramic material to the mixture and then dispersing it to obtain a suspension; and removing the solvent from the suspension to obtain the thermally conductive phase change material.

[0016] Preferably, the melt phase change coating method includes the following steps: mixing the heat sensitizer and the thermal conductive agent and performing a melt treatment to obtain a melt mixture; adding the ceramic material to the melt mixture and performing a blending and dispersion treatment to obtain the thermally conductive phase change material.

[0017] A third aspect of the present invention provides a diaphragm, the diaphragm comprising a diaphragm substrate and a coating layer coated on at least one surface of the diaphragm substrate, the coating layer comprising a thermally conductive phase change material, the thermally conductive phase change material being the thermally conductive phase change material provided in the first aspect of the present invention.

[0018] Preferably, the loading of the thermally conductive phase change material on the surface of the diaphragm substrate is 1 mg / cm³. 2 -10mg / cm 2 .

[0019] Preferably, the coating thickness is 1μm-20μm.

[0020] The fourth aspect of the present invention provides the application of the above-mentioned thermally conductive phase change material or the above-mentioned separator in ion system batteries and secondary batteries.

[0021] The thermally conductive phase change material provided by this invention has high thermal conductivity and rapid thermal response. It can quickly undergo a melting phase change when heated, cutting off the ion transport process in the ion system battery, effectively preventing and stopping battery thermal runaway, and improving battery safety. Furthermore, the thermally conductive phase change material provided by this invention will not undergo physical / chemical reactions with the electrolyte to produce phenomena such as dissolution or swelling. It is easy to form a microporous layer, is non-toxic and non-polluting, does not contain any rare elements, and has a significant price advantage.

[0022] The thermally conductive phase change material-coated separator provided by this invention, when applied in ion-electric batteries, can block the separator pores and inhibit the ion transport channels under high temperature or short-circuit conditions, thereby blocking the reaction process of the ion-electric battery, effectively preventing and stopping the occurrence of thermal runaway in the ion-electric battery, and improving the safety of the battery.

[0023] The ion system battery or secondary battery containing the above-mentioned thermally conductive phase change material or separator provided by the present invention has the advantages of fast thermal response, good pore-closure effect, high safety, high power, strong adaptability, long cycle life, low cost, simple maintenance, and environmental protection. It is suitable for use as a large-scale energy storage device in wind power, hydropower, tidal power, and solar power generation systems or as a power battery in mobile vehicles. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the working principle of the thermally conductive phase change material provided in a specific embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a lithium-ion battery structure provided by the present invention according to some preferred embodiments;

[0026] Figure 3 This is a charge-discharge curve of a lithium-ion battery at room temperature provided in a specific embodiment of the present invention;

[0027] Figure 4 This is a charge-discharge curve of a lithium-ion battery at 120°C provided in a specific embodiment of the present invention.

[0028] Figure 5 This is a graph showing the temperature change of a lithium-ion battery under short-circuit conditions, provided in a specific embodiment of the present invention. Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] As previously stated, the first aspect of the present invention provides a thermally conductive phase change material, the thermally conductive phase change material having a core-shell structure, comprising a ceramic material as the core and a shell layer covering the surface of the core, the shell layer comprising a thermosensitive agent and a thermally conductive agent, the mass ratio of the thermosensitive agent to the thermally conductive agent being (1-50):1, and the mass ratio of the core to the shell layer being (8-500):1.

[0031] The thermally conductive phase change material provided by this invention has high thermal conductivity and rapid thermal response. It will not undergo physical / chemical reactions with the electrolyte to produce phenomena such as dissolution or swelling. It is easy to form a microporous layer, is non-toxic and pollution-free, does not contain any rare elements, and has a significant price advantage.

[0032] The thermally conductive phase change material provided by this invention allows the thermally conductive agent in the shell to rapidly transfer heat to the thermosensitive agent when the ambient temperature is too high or the battery is short-circuited. This causes the thermosensitive agent to melt rapidly, and the thermosensitive agent forms one or more isolation layers in the microporous channels of the ceramic material, on the surface of the separator substrate, and inside the separator. This effectively blocks the free passage of ions in the ion system battery, closes the ion transport channels in the battery, and cuts off the battery reaction, effectively preventing and stopping the occurrence of battery thermal runaway and greatly improving the safety of the ion system battery.

[0033] It should be noted that the present invention does not have any special requirements for the type of ceramic material. According to some preferred embodiments of the present invention, the ceramic material is at least one of boehmite and alumina ceramic.

[0034] According to some preferred embodiments of the present invention, the heat sensitizer is at least one selected from polyethylene, thermoplastic polyurethane rubber, and ethylene-vinyl acetate copolymer. The aforementioned heat sensitizer does not chemically react with the electrolyte, is a thermoplastic polymer with phase change properties, and has a wide phase change temperature range of 100°C-150°C. When the battery experiences thermal abuse and the temperature rises to 100°C-150°C, the heat sensitizer can respond rapidly, transforming into a molten state and sealing the separator pores, interrupting the ion transport process in the battery, and preventing thermal runaway.

[0035] According to some preferred embodiments of the present invention, the thermally conductive agent is at least one selected from diamond, graphite, carbon powder, graphene, carbon nanotubes, aluminum nitride, aluminum oxide, boron nitride, and zinc oxide. The inventors of the present invention have discovered that the thermally conductive phase obtained by mixing the above-mentioned thermally conductive agent with a heat sensitizer has higher thermal conductivity, faster thermal response speed, and better sealing effect on diaphragm pores under high-temperature conditions and short-circuit conditions compared to using the heat sensitizer alone as the thermally conductive phase.

[0036] According to some particularly preferred embodiments, the average particle size of the thermal conductive agent is 10nm-500nm, preferably 10nm-100nm. Thermally conductive phase change materials made from thermal conductive agents in this particle size range have higher thermal conductivity and faster thermal response.

[0037] According to some preferred embodiments of the present invention, the thermal conductive agent is a composition of carbon powder, alumina, and boron nitride in a mass ratio of 1:(0.3-0.8):(0.1-0.5). The inventors of the present invention have discovered that a thermal conductive agent with specific components and a specific ratio range produces a thermally conductive phase change material with higher thermal conductivity and faster thermal response. When applied in ion-ion batteries, it can interrupt the ion transport process in the separator of the ion battery within a second-level time frame when thermal abuse occurs, preventing thermal runaway.

[0038] According to some preferred embodiments of the present invention, the thermally conductive phase change material is a thermally conductive phase change microsphere, and the average particle size of the thermally conductive phase change microsphere is 1000nm-5000nm. Exemplarily, the average particle size of the thermally conductive phase change microsphere can be 1000nm, 2000nm, 2500nm, 3000nm, or 5000nm.

[0039] According to some preferred embodiments of the present invention, the average thickness of the shell layer is 100nm-1000nm, preferably 100nm-500nm. Exemplarily, the average thickness of the shell layer can be 100nm, 150nm, 250nm, 300nm, 500nm, or 1000nm.

[0040] like Figure 1 As shown in the diagram, the working principle of the thermally conductive phase change microspheres provided by this invention is such that, under high environmental conditions or high temperatures caused by short circuits, the heat-sensitive agent in the shell layer of the thermally conductive phase change material can quickly respond thermally, transform into a molten state, and block the pores of the separator, inhibiting the ion transport channels of the separator, blocking the reaction process of the battery, avoiding thermal runaway of the battery, and improving the safety of the battery.

[0041] A second aspect of the present invention provides a method for preparing the thermally conductive phase change material provided in the first aspect, comprising the following steps:

[0042] The thermally conductive phase change material is obtained by coating a shell containing a heat-sensitive agent and a thermally conductive agent onto the surface of a ceramic material that serves as the core using a solution coating method or a melt phase change coating method.

[0043] In the shell layer, the mass ratio of the heat sensitizer to the thermally conductive agent is (1-50):1; in the thermally conductive phase change material, the mass ratio of the core to the shell layer is (8-500):1.

[0044] According to some preferred embodiments of the present invention, the solution coating method includes the following steps: mixing the heat sensitizer and the thermal conductive agent in an organic solvent to obtain a mixture; adding the ceramic material to the mixture and then dispersing it to obtain a suspension; and removing the solvent from the suspension to obtain the thermally conductive phase change material.

[0045] It should be noted that the present invention does not have any special limitation on the type of organic solvent, as long as it does not chemically react with the heat sensitizer, thermal conductive agent and ceramic material. For example, the organic solvent described in the present invention is N,N-dimethylacetamide.

[0046] It should be noted that the present invention does not impose any particular restrictions on the specific method of the mixing process, as long as the heat-sensitive agent and the heat-conducting agent can be fully and evenly mixed. For example, the mixing process described in the present invention is a stirring mixing process.

[0047] It should be noted that the present invention does not impose any particular limitation on the specific method of dispersion treatment, as long as the ceramic material can be fully dispersed in the mixture. For example, the dispersion treatment described in the present invention is ultrasonic dispersion treatment.

[0048] It should be noted that the present invention does not particularly limit the specific method of solvent removal treatment, as long as the organic solvent can be removed without affecting the chemical properties of the thermally conductive phase change material. For example, the solvent removal treatment can be vacuum heating drying or spray drying.

[0049] According to some more preferred embodiments of the present invention, the solution coating method further includes the following step: dispersing the thermally conductive phase change material using a ball mill to obtain thermally conductive phase change microspheres. It should be noted that the present invention does not have special requirements for the ball milling rate; it can be adjusted accordingly based on the required microsphere size.

[0050] According to some preferred embodiments of the present invention, the melt phase change coating method includes the following steps: mixing the heat sensitizer and the thermal conductive agent and performing a melt treatment to obtain a melt mixture; adding the ceramic material to the melt mixture and performing a blending and dispersion treatment to obtain the thermally conductive phase change material.

[0051] It should be noted that the present invention does not impose any particular limitation on the specific method of the melting treatment, as long as it can transform the mixture of the heat-sensitive agent and the thermally conductive agent into a molten state. For example, the heat-sensitive agent and the thermally conductive agent are subjected to high-temperature heating treatment at the melting temperature of the heat-sensitive agent, thereby transforming the mixture of the heat-sensitive agent and the thermally conductive agent into a molten state.

[0052] It should be noted that the purpose of the blending and dispersion treatment is to fully disperse the ceramic material in the molten mixture, so that the molten heat-sensitive agent and thermally conductive agent can fully coat the surface of the ceramic material to form a core-shell structured thermally conductive phase change material. Therefore, the present invention does not particularly limit the specific method of blending and dispersion treatment; for example, mechanical blending can be used.

[0053] According to some more preferred embodiments of the present invention, the melt phase change coating method further includes the following steps:

[0054] The thermally conductive phase change material is dispersed using a ball mill to obtain thermally conductive phase change microspheres. It should be noted that this invention does not have specific requirements for the ball milling rate; it can be adjusted according to the required microsphere size.

[0055] A third aspect of the present invention provides a diaphragm, the diaphragm comprising a diaphragm substrate and a coating layer coated on at least one surface of the diaphragm substrate, the coating layer comprising a thermally conductive phase change material, the thermally conductive phase change material being the thermally conductive phase change material provided in the first aspect of the present invention.

[0056] The separator provided by this invention is coated with the thermally conductive phase change material provided by this invention. It has good compatibility with existing lithium-ion battery manufacturing systems and can be directly introduced into the production system. It has low processing costs. Lithium-ion batteries made with the separator provided by this invention have high thermal conductivity, rapid thermal response, are not prone to thermal runaway, and have high battery safety.

[0057] Furthermore, the separator provided by the present invention has no other additional coating layer. The thermally conductive phase change microspheres provided by the present invention can form a microporous structure on the surface of the separator substrate, which will not affect the ion transport performance of the lithium-ion battery, and can also enhance the thermal response rate of the lithium-ion battery. In the event of thermal abuse of the lithium-ion battery, the ion transport channel can be cut off in time to prevent thermal runaway of the battery and improve the safety performance of the battery.

[0058] According to some preferred embodiments of the present invention, the loading of the thermally conductive phase change material on the surface of the diaphragm substrate is 1 mg / cm². 2 -10mg / cm 2 .

[0059] According to some preferred embodiments of the present invention, the coating thickness of the coating layer is 1μm-20μm. It should be noted that the present invention does not have special requirements on the coating method of the coating layer; for example, spraying, dip coating, extrusion coating, and transfer coating are all acceptable methods.

[0060] According to some preferred embodiments of the present invention, the coating layer further comprises a dispersing agent, wherein the mass ratio of the thermally conductive phase change material to the dispersing agent is 100:(1-10).

[0061] According to some more preferred embodiments of the present invention, the dispersing agent is at least one of styrene-butadiene rubber and sodium carboxymethyl cellulose.

[0062] The fourth aspect of the present invention provides the application of the above-mentioned thermally conductive phase change material or the above-mentioned separator in ion system batteries and secondary batteries.

[0063] According to some preferred embodiments of the present invention, a lithium-ion battery is prepared by assembling a separator coated with the thermally conductive phase change material provided by the present invention, along with positive and negative electrodes and an electrolyte, etc. The lithium-ion battery has good thermal responsiveness and high safety.

[0064] According to some preferred embodiments of the present invention, the structural schematic diagram of the assembled lithium-ion battery is shown below. Figure 2 As shown, a lithium-ion battery is obtained by sequentially assembling a positive current collector, a positive electrode, a thermistor-responsive separator, a negative electrode, and a negative current collector. The thermistor-responsive separator is a separator coated with the thermally conductive phase change material described in this invention.

[0065] The present invention will be described in detail below through examples. Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0066] N,N-Dimethylacetamide, analytical grade, 99.0%, purchased from Aladdin Company;

[0067] Thermoplastic polyurethane rubber, purchased from Bayer Group in Germany, grade 192X;

[0068] Ethylene-vinyl acetate copolymer, purchased from Formosa Plastics Group, Taiwan, China, grade 7350M;

[0069] Polyethylene, purchased from Maoming Petrochemical Company, grade 2426H;

[0070] The toner, with a purity of 99.5% and an average particle size of 30 nm, was purchased from Aladdin Company.

[0071] Graphite, 99.9% purity, average particle size 100nm, purchased from Qingdao Furuit Graphite Co., Ltd.

[0072] Boehmite, purchased from Anhui Yishitong Materials Technology Co., Ltd., grade BG-613.

[0073] Example 1

[0074] Preparation of thermally conductive phase change microspheres A1 by solution coating method:

[0075] (1) The heat sensitizer and the heat conductor are mixed in an organic solvent to obtain a mixture. Specifically, 30g of thermoplastic polyurethane rubber and 8g of carbon powder with an average particle size of 30nm are stirred and mixed evenly in 700ml of N,N-dimethylacetamide to obtain a mixture.

[0076] (2) After adding the ceramic material to the mixture, a dispersion treatment is performed to obtain a suspension. Specifically, 600g of boehmite is added to the mixture and stirred to disperse evenly to obtain the suspension.

[0077] (3) The suspension is subjected to solvent removal treatment to obtain the thermally conductive phase change material. Specifically, the solvent in the suspension is removed by oven drying technology, and the powdered thermally conductive phase change microspheres A1 are obtained by ball milling.

[0078] The performance parameters of the thermally conductive phase change microspheres A1 are shown in Table 1.

[0079] Example 2

[0080] Preparation of thermally conductive phase change microspheres A2 by solution coating method:

[0081] The difference is that the heat sensitizer is ethylene-vinyl acetate copolymer, and the thermal conductive agent is alumina with an average particle size of 100 nm. The rest of the preparation process and specific parameters are the same as in Example 1, and thermally conductive phase change microspheres A2 are obtained.

[0082] The performance parameters of the thermally conductive phase change microsphere A2 are shown in Table 1.

[0083] Example 3

[0084] Preparation of thermally conductive phase change microspheres A3 by solution coating method:

[0085] The difference is that the thermal conductive agent is a composition of carbon powder, alumina and boron nitride, wherein the mass ratio of carbon powder, alumina and boron nitride is 1:0.5:0.3. The rest of the preparation process and specific parameters are the same as in Example 1, and thermally conductive phase change microspheres A3 are obtained.

[0086] The performance parameters of the thermally conductive phase change microspheres A3 are shown in Table 1.

[0087] Example 4

[0088] Preparation of thermally conductive phase change microspheres A4 by melt phase change coating method:

[0089] (1) The heat sensitizer and the heat conductor are mixed and melted to obtain a molten mixture. Specifically, 50g of polyethylene and 10g of graphite are melted and ground and mixed evenly to obtain a molten mixture of polyethylene and graphite.

[0090] (2) The ceramic material is added to the molten mixture and ground to obtain the thermally conductive phase change microspheres. Specifically, 600g of boehmite is added to the molten mixture and stirred and dispersed evenly. The mixture is then dried in an oven and ball-milled to obtain powdered thermally conductive phase change microspheres A4.

[0091] The performance parameters of the thermally conductive phase change microspheres A4 are shown in Table 1.

[0092] Example 5

[0093] Preparation of thermally conductive phase change microspheres A5 by melt phase change coating method:

[0094] The difference is that the amount of polyethylene used is 30g and the amount of graphite is 10g. The rest of the preparation process and specific parameters are the same as in Example 4, and thermally conductive phase change microspheres A5 are obtained.

[0095] The performance parameters of the thermally conductive phase change microsphere A5 are shown in Table 1.

[0096] Comparative Example 1

[0097] The difference is that no thermal conductive agent is added, and the rest of the preparation process and specific parameters are the same as in Example 1, to obtain phase change microspheres D1.

[0098] The performance parameters of phase change microsphere D1 are shown in Table 1.

[0099] Comparative Example 2

[0100] Boehmite without a shell, after ball milling, is designated as microsphere D2.

[0101] The performance parameters of microsphere D2 are shown in Table 1.

[0102] The thermal conductivity of the thermally conductive phase change microspheres in the examples and comparative examples was measured using a NETZSCH LFA467HyperFlash laser flare instrument, as shown in Table 1.

[0103] Table 1

[0104] Heat saturator: Thermal conductive agent (mass ratio) 15:4 15:4 15:4 5:1 8：1 / / Core: Shell (mass ratio) 300:19 300:19 300:19 100:1 15:1 100：5 / Shell thickness / nm 411 526 430 363 870 384 / Average particle size / μm 2.4 2.5 2.4 2.3 2.9 2.3 2.0 <![CDATA[Thermal conductivity / W·m -1 K -1 > 0.51 0.36 0.7 0.29 0.3 0.20 24

[0105] As can be seen from Table 1, the thermal conductivity of the thermally conductive phase change microspheres prepared in the embodiments of the present invention is significantly higher than that of the phase change microsphere D1 prepared in Comparative Example 1. Although the thermal conductivity of the thermally conductive phase change microspheres prepared in the embodiments of the present application is lower than that of the microsphere D2 prepared in Comparative Example 2, the microsphere D2 does not have phase change properties and cannot prevent or stop the thermal runaway of the battery.

[0106] Test example:

[0107] (1) Preparation of the diaphragm:

[0108] 10,000 g of microspheres, 800 g of styrene-butadiene rubber and 500 g of sodium carboxymethyl cellulose were added to 20,000 g of water and mixed evenly to obtain a slurry. The slurry was then coated onto the surface of the diaphragm substrate and dried to obtain the diaphragm.

[0109] Specifically, the membrane substrate is a wet membrane substrate with a thickness of 12 μm, and the coating method of the mixed slurry is single-sided coating with a coating thickness of 3 μm;

[0110] (2) Preparation of lithium-ion batteries:

[0111] A lithium-ion battery is obtained by encapsulating the separator with the positive electrode, negative electrode, positive electrode current collector and negative electrode current collector, and the selection of the positive electrode, negative electrode, positive electrode current collector and negative electrode current collector makes the rated capacity of the lithium-ion battery 50Ah.

[0112] The microspheres are thermally conductive phase change microspheres prepared in the examples, phase change microspheres D1 prepared in Comparative Example 1, and microspheres D2 prepared in Comparative Example 2. The lithium-ion batteries prepared are denoted as L1, L2, L3, L4, L5, DL1, and DL2, respectively.

[0113] Internal resistance test: The lithium-ion batteries prepared above were subjected to DC internal resistance tests at different temperatures, and the results are shown in Table 2 below.

[0114] Table 2

[0115] 25℃ / mΩ 1.768 1.741 1.734 1.755 1.733 1.741 1.712 120℃ treatment for 1 minute / mΩ 14.245 15.212 18.135 12.123 13.821 2.212 1.721 120℃ treatment for 10 minutes / mΩ 22.126 21.764 28.321 18.091 19.031 16.231 1.723

[0116] As shown in Table 2, the lithium-ion battery coated with the thermally conductive phase change microspheres prepared in the embodiments of the present invention is more sensitive to temperature response and exhibits good thermal responsiveness within 10 minutes. Under thermistor temperature conditions, the battery internal resistance can change more rapidly, suppressing the occurrence of battery thermal runaway.

[0117] High-temperature charge-discharge test: The lithium-ion batteries prepared above were subjected to high-temperature charge-discharge tests. The test process involved charging and discharging the fully charged cells obtained after charging and discharging the lithium-ion batteries in an environment of 120°C. The results are shown in Table 3 below.

[0118] Table 3

[0119] Charging capacity (Ah) 32.0 33.8 29.9 35.2 38.7 41.2 43.8 Discharge capacity (Ah) 31.4 31.6 28.4 34.8 38.1 40.0 43.5

[0120] As shown in Table 3, the lithium-ion battery coated with the thermally conductive phase change microspheres prepared in the embodiments of the present invention will have a significantly reduced capacity under high temperature conditions, which will reduce the release of battery energy, prevent battery thermal runaway, and effectively improve the safety of lithium-ion batteries under high temperature conditions.

[0121] For example, L1, L2, L3, L4, L5, DL1, and DL2 were charged and discharged at room temperature, and the resulting battery charge and discharge curves are shown in the figure. Figure 3 As shown; L1, L2, L3, L4, L5, DL1, and DL2 were charged and discharged at 120℃, and the resulting battery charge and discharge curves are shown in the figure. Figure 4 As shown. By Figure 3 and Figure 4 It can be seen that, compared with normal temperature conditions, the battery capacity of L1-L5 decreases significantly under high temperature conditions. Moreover, the decrease in battery capacity is much greater than that of DL1 and DL2 under high temperature conditions. This indicates that the lithium-ion battery provided in this embodiment of the invention has good thermal sensitivity and can stop the ion transport process in the battery under high temperature conditions, thus preventing thermal runaway of the battery.

[0122] Short circuit test: The lithium-ion batteries prepared above were subjected to short circuit tests to measure the surface temperature of the batteries under 100% charge. The test results are shown in Table 4 below.

[0123] Table 4

[0124] Maximum temperature / °C 130 124 224 312

[0125] A short circuit causes a rapid increase in internal heat within the battery. As shown in Table 4, the lithium-ion battery prepared in this embodiment of the invention can generate a more rapid thermal response, and its maximum temperature under short-circuit conditions is significantly lower than that of the comparative lithium-ion battery. For example, Figure 5 The graph shows the battery temperature change curves of L1, L3, DL1, and DL2 under short-circuit conditions, as shown below. Figure 5 As shown, the lithium-ion battery in Comparative Example 1 has difficulty cutting off the ion transport process in time, with a maximum temperature of 224°C under short-circuit conditions. The battery in Comparative Example 2 has no thermosensitive response, with a maximum temperature of 312°C. Therefore, the lithium-ion battery prepared in this embodiment of the invention exhibits excellent thermosensitive response, better cutting off the ion transport process under abnormal operating conditions and improving battery safety.

[0126] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A thermally conductive phase change material, characterized in that, The thermally conductive phase change material has a core-shell structure, comprising a ceramic material as the core and a shell layer covering the surface of the core. The shell layer contains a thermosensitive agent and a thermally conductive agent, with the mass ratio of the thermosensitive agent to the thermally conductive agent being (1-50):1, and the mass ratio of the core to the shell layer being (8-500):

1. The thermally conductive agent is a composition of carbon powder, alumina, and boron nitride in a mass ratio of 1:(0.3-0.8):(0.1-0.5).

2. The thermally conductive phase change material according to claim 1, characterized in that, The ceramic material is at least one of boehmite and alumina ceramics; And / or, the heat sensitizer is at least one of polyethylene, thermoplastic polyurethane rubber, and ethylene-vinyl acetate copolymer.

3. The thermally conductive phase change material according to claim 1 or 2, characterized in that, The thermally conductive phase change material is a thermally conductive phase change microsphere, the average particle size of the thermally conductive phase change microsphere is 1000nm-5000nm, and the average thickness of the shell is 100nm-1000nm.

4. A method for preparing a thermally conductive phase change material according to any one of claims 1-3, characterized in that, Includes the following steps: The thermally conductive phase change material is obtained by coating a shell containing a heat-sensitive agent and a thermally conductive agent onto the surface of a ceramic material that serves as the core using a solution coating method or a melt phase change coating method. In the shell layer, the mass ratio of the heat-sensitive agent to the thermally conductive agent is (1-50):1; in the thermally conductive phase change material, the mass ratio of the core to the shell layer is (8-500):

1.

5. The preparation method according to claim 4, characterized in that, The solution coating method includes the following steps: mixing the heat sensitizer and the thermally conductive agent in an organic solvent to obtain a mixture; adding the ceramic material to the mixture and then dispersing it to obtain a suspension; and removing the solvent from the suspension to obtain the thermally conductive phase change material. And / or, the melt phase change coating method includes the following steps: mixing the heat sensitizer and the thermal conductive agent and performing a melt treatment to obtain a melt mixture; adding the ceramic material to the melt mixture and performing a blending and dispersion treatment to obtain the thermally conductive phase change material.

6. A diaphragm, characterized in that, The diaphragm includes a diaphragm substrate and a coating layer applied to at least one surface of the diaphragm substrate, the coating layer comprising a thermally conductive phase change material. The thermally conductive phase change material is the thermally conductive phase change material according to any one of claims 1-3.

7. The diaphragm according to claim 6, characterized in that, The loading of the thermally conductive phase change material on the surface of the diaphragm substrate is 1 mg / cm². 2 -10mg / cm 2 ; And / or, the coating thickness of the coating layer is 1μm-20μm.

8. The application of the thermally conductive phase change material according to any one of claims 1-3 or the separator according to claim 6 or 7 in ion-based batteries and secondary batteries.

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