Anisotropic heat-conducting flame-retardant cell spacer and preparation method thereof

Abstract

The application provides an anisotropic heat-conducting flame-retardant cell spacer and a preparation method thereof. The cell spacer is a BNNS / kaolin composite cellulose-based cell spacer, which is formed by alternately stacking a plurality of BNNS layers and a plurality of kaolin nanolayers, and the heat-conducting flame-retardant cell spacer is regularly oriented along the horizontal direction, and has anisotropic heat conduction and double efficient flame-retardant characteristics. The material integrates anisotropic heat conduction, extreme point heat source stability and flame-retardant characteristics, and provides a feasible technical path for solving the thermal management bottleneck of high-safety demand lithium batteries.

Description

Technical Field

[0001] This application belongs to the field of battery thermally conductive composite material technology, and particularly relates to an anisotropic thermally conductive and flame-retardant battery cell spacer and its preparation method. Background Technology

[0002] With the continuous development of energy storage technology, the requirements for high-energy-density energy storage systems and their safety performance are also increasing. During the operation of high-density energy storage systems, the cells inevitably generate heat. If this heat cannot be dissipated to the environment in time, heat accumulation can easily occur, leading to thermal runaway. Mithal's research indicates that for every 1°C decrease in the temperature of electronic components from their normal operating temperature, the failure rate can be reduced by 4%; however, when the temperature increases by 10-20°C from the normal level, the failure rate increases by 100%. Simultaneously, the flame-retardant and fire-resistant performance requirements under extreme conditions such as cell short circuits and collisions have become key challenges. Furthermore, with the increasing demand for lightweight and miniaturized designs, flexible, lightweight, and environmentally friendly materials are more likely to meet these requirements. Therefore, the cell spacer, as a crucial protective component of the energy storage battery pack, must simultaneously meet the core requirements of rapidly dissipating heat from the cells, delaying heat diffusion, and suppressing flame spread.

[0003] In fact, heat accumulation has become one of the most frequent failure risks in highly integrated electronic devices and high-energy-density energy storage, posing a severe challenge to the reliability of electronic equipment, the safety of new energy devices, and the stable development of the industry. Therefore, effectively mitigating heat accumulation and curbing thermal runaway and thermal diffusion has become a key industrial problem that urgently needs to be solved in the electronics and new energy fields. However, existing battery cell spacers mostly use rubber and plastic materials, which have problems such as low thermal conductivity, inability to simultaneously achieve in-plane heat dissipation and out-of-plane insulation, and insufficient flame retardant properties.

[0004] To improve performance, researchers have attempted to modify the material by adding thermally conductive fillers and flame retardants. Patent CN112552681 A discloses a functionalized boron nitride nanosheet / MXene / polybenzimidazole high thermal conductivity composite film and its preparation method. This invention utilizes electrostatic self-assembly on a polybenzimidazole framework, with BNNS and MXene serving as a self-supporting framework to construct the composite film. At a filler content of 10 wt%, the system achieves a maximum thermal conductivity of 10 W / (m·K). However, because this film is prepared by filtration of a mixed solution, the arrangement of BNNS and MXene cannot be controlled; it only ensures a stacked structure, failing to balance in-plane heat dissipation and out-of-plane thermal insulation, resulting in insufficient flame retardant performance. In literature research, a hexagonal boron nitride ink was designed to impregnate natural plant fibers, achieving excellent flame retardant effects and mechanical properties. This design increased the thermal conductivity of the substrate to 0.242 W / (m·K) while achieving high flame retardancy and mechanical properties, but still could not adequately meet heat dissipation requirements. Summary of the Invention

[0005] This application addresses the aforementioned issues and aims to provide an anisotropic thermally conductive and flame-retardant BNNS cell spacer and its preparation method. This thermally conductive and flame-retardant BNNS cell spacer is a BNNS / kaolin composite cellulose-based cell spacer, consisting of multiple BNNS layers and multiple kaolin layers self-assembled and alternately stacked, forming a composite cellulose-based cell spacer with a dual flame-retardant mechanism. The anisotropy coefficient reaches 23.39 (in-plane thermal conductivity of 5.38 W / (m·K), out-of-plane thermal conductivity of 0.23 W / (m·K)). In extreme high-temperature thermal source stability tests at 450℃, this material exhibits defects in 72 seconds, superior to uniform thermal management materials, providing a critical window for delaying thermal diffusion. During high-rate charging of lithium batteries, it reduces the battery operating temperature by 19.4%, and extends the thermal diffusion time in single-cell thermal runaway trigger tests from 34 seconds in the blank group to 225 seconds, providing sufficient time for battery pack safety warnings and emergency handling. Due to the synergistic effect of its components, this material exhibits self-extinguishing behavior in the event of lithium battery electrolyte leakage.

[0006] The first aspect of this application provides an anisotropic thermally conductive and flame-retardant battery cell spacer, which is formed by the alternating stacking of BNNS layers and kaolin nanolayers on cellulose paper through self-assembly. The BNNS nanosheets on the BNNS layers polymerize a halogen-free phosphorus flame retardant through π-π conjugation to form a composite cellulose-based battery cell spacer.

[0007] In any embodiment, the loading of the BNNS layer and the kaolin nanolayer on the cellulose paper is 10-40%.

[0008] In any embodiment, the kaolin nanolayer is a kaolin nanosheet.

[0009] In any embodiment, the size of a single nanosheet in the BNNS layer is 1µm-20µm; the size of a single nanosheet in the kaolin nanolayer is 1µm-20µm.

[0010] In any embodiment, the total number of BNNS layers and kaolin nanolayers is 50-70 layers.

[0011] A second aspect of this application also provides a method for preparing an anisotropic thermally conductive and flame-retardant battery cell spacer, comprising the following steps:

[0012] (1) The cellulose paper was alternately washed and dried in anhydrous ethanol and deionized water;

[0013] (2) The cellulose paper was soaked in BNNS solution to obtain a BNNS layer, and then dried to obtain a BNNS layer adsorbed by non-covalent bonding.

[0014] (3) The cellulose paper with the BNNS layer was impregnated with the kaolin nanosheet dispersion to obtain the kaolin nanolayer, and then dried to obtain the kaolin layer adsorbed by non-covalent bond interaction.

[0015] (4) Alternately repeat steps (2) and (3) to alternately coat the positively and negatively charged solutions until the required number of deposition cycles is reached, and a composite cellulose-based battery spacer is obtained.

[0016] In any embodiment, step (4) further includes a crosslinking step, in which the composite cellulose-based battery cell spacer is soaked in sodium tripolyphosphate for a period of time and then dried.

[0017] In any embodiment, the sodium tripolyphosphate soaking concentration is 1 mg / ml-10 mg / ml, and the soaking time is 1-12 hours.

[0018] In any embodiment, steps (2) and (3) are performed using layer-by-layer self-assembly (LBL) coating, wherein the single immersion time in the LBL is 1 min to 10 min, and the drying temperature is 40°C to 80°C. Preferably, the single immersion time is 2 min, and the drying temperature is 60°C.

[0019] In any embodiment, the concentration ratio of the BNNS solution to the kaolin nanosheet dispersion is 1:2-4:1.

[0020] In any embodiment, the concentration of the BNNS solution is 1 mg / ml to 10 mg / ml; the concentration of the kaolin nanosheet dispersion is 1 mg / ml to 10 mg / ml.

[0021] In any embodiment, the kaolin nanosheet dispersion is prepared by adding kaolin powder to deionized water after dispersing chitosan, followed by 1 hour of ultrasonication in a water bath and 2 hours of mechanical stirring to obtain the kaolin nanosheet dispersion.

[0022] In any embodiment, the preparation of the BNNS solution is as follows: boron nitride nanosheets (BNNS) are ultrasonically dissolved in 0.5 mg / ml-5 mg / ml sodium carboxymethyl cellulose in an ice bath for 1 hour to obtain a uniformly dispersed BNNS solution; a halogen-free phosphorus flame retardant is added to the obtained uniformly dispersed BNNS solution and polymerized for 6-24 hours; the solid content of the halogen-free phosphorus flame retardant to BNNS is 2:1-1:4.

[0023] In any embodiment, the boron nitride nanosheets (BNNS) are prepared as follows: Hexagonal boron nitride powder (h-BN) is dispersed in a strongly alkaline alcohol-water mixture and hydrothermally treated at 160°C for 4 hours; the hydroxylated reaction solution is centrifuged and washed 3-6 times until the pH is below 9, and the supernatant is discarded; the precipitate after centrifugation is dispersed in a mixture of isopropanol and deionized water, and ultrasonically treated in a water bath for 4 hours to obtain the BNNS reaction solution; the reaction solution is centrifuged and dried to obtain BNNS nanosheets. The ratio of anhydrous ethanol to deionized water in the alcohol-water mixture is 135 ml:165 ml. The ratio of isopropanol to deionized water in the isopropanol-deionized water mixture is 1:1.

[0024] The advantages of this invention compared to the prior art are:

[0025] 1) The synergistic construction of anisotropic structure and flame retardant system can quickly dissipate local heat through efficient in-plane heat conduction in the case of local thermal defects, suppress heat spread by relying on out-of-plane directional heat insulation, and combined with flame retardant protection, avoid the deepening of material thermal damage and ensure its structural and performance stability.

[0026] 2) By orderly arranging the thermally conductive and thermally insulating layers, while BNNS forms a thermally conductive path, the anisotropy of the nanocomposite material is improved through effective control of the thermally insulating layers, thus meeting the thermal management requirements of electronic devices such as lithium batteries.

[0027] 3) Adding nitrogen and phosphorus compounds as flame retardants, the "condensed phase + gas phase" dual flame retardant mechanism improves the flame retardancy of nanocomposite materials and provides a critical window for delaying heat diffusion. Attached Figure Description

[0028] Figure 1 The image shows the microstructure of an anisotropic thermally conductive and flame-retardant battery cell spacer prepared in Example 1. Image a is a scanning electron microscope (SEM) image of the cross-section of the battery cell spacer; image b is a SEM image of the nanosheet arrangement on the fibers of the battery cell spacer; and image c is an enlarged schematic diagram of part b.

[0029] Figure 2 The anisotropic thermal conductivity of the thermally conductive and flame-retardant battery cell spacer prepared in Example 1 and the battery cell spacer prepared in Comparative Example 1 are shown.

[0030] Figure 3 The deformation-stress curves are shown for the thermally conductive and flame-retardant battery cell spacer prepared in Example 1 and the battery cell spacer prepared in Comparative Example 1. Detailed Implementation

[0031] The following detailed description, with appropriate reference to the accompanying drawings, discloses an embodiment of an anisotropic thermally conductive and flame-retardant battery cell spacer and its preparation method. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0032] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0037] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] To address the problems in the background technology, the inventors have weakened heat transfer between devices through directional thermal insulation; and enhanced heat dissipation to the environment through efficient heat dissipation, avoiding continuous heat accumulation, while ensuring that the dissipation of heat does not affect adjacent electronic devices. Boron nitride nanosheets (BNNS) are ideal thermally conductive fillers due to their ultra-high thermal conductivity and insulation properties, while kaolin nanosheets provide medium- and high-temperature thermal insulation and structural stability. Hexaphenoxycyclotriphosphazene (HPCTP) and boron nitride nanosheets (BNNS) exhibit excellent synergistic flame-retardant effects. However, in existing modification technologies, the functional components have poor dispersibility and are prone to agglomeration, making it difficult to form a directional thermally conductive network and a stable flame-retardant structure that meet the requirements of cell spacing. Furthermore, the preparation process is complex and costly, failing to meet the needs of large-scale application of power batteries.

[0039] Layer-by-layer self-assembly can achieve ordered and directional loading of functional components, improving dispersion and the stability of the composite system. Therefore, combining this method with the anisotropic thermal conductivity of BNNS and the synergistic flame-retardant system of NP to prepare anisotropic thermally conductive and flame-retardant cell spacers suitable for energy storage systems has significant practical implications for improving the safety performance of power batteries.

[0040] This invention utilizes flame-retardant polymerized BNNS nanosheets and kaolin nanosheets as assembly units, and prepares anisotropic thermally conductive and flame-retardant BNNS battery cell spacers through layer-by-layer self-assembly and interfacial cross-linking. The BNNS layers and kaolin nanolayers are arranged in an orderly manner along the planar direction to construct thermally conductive pathways. The resulting anisotropic thermally conductive and flame-retardant BNNS film achieves an anisotropy coefficient of 23.39 (in-plane thermal conductivity of 5.38 W / (m·K), and out-of-plane thermal conductivity of 0.23 W / (m·K)). The halogen-free phosphorus-based flame retardant polymerizes with the BNNS nanosheets through π-π conjugation. The resulting anisotropic thermally conductive and flame-retardant BNNS battery cell spacer exhibits self-extinguishing behavior in the event of lithium battery electrolyte leakage. "In-plane" refers to the direction of the material plane, i.e., the horizontal direction of the film; "out-of-plane" refers to the direction outside the material plane, i.e., the vertical direction of the film.

[0041] In one embodiment of this application, an anisotropic thermally conductive and flame-retardant battery cell spacer is proposed, which is formed by the alternating stacking of BNNS layers and kaolin nanolayers on cellulose paper through self-assembly. The BNNS nanosheets on the BNNS layers polymerize halogen-free phosphorus flame retardants through π-π conjugation to form a composite cellulose-based battery cell spacer.

[0042] By using a kaolin layer with low thermal conductivity as an insulation layer and BNNS as a thermally conductive layer, the two components are stacked layer by layer to achieve thermal insulation in the vertical direction and high thermal conductivity in the horizontal direction.

[0043] The BNNS layer and the kaolin nanolayer are solutions with positive and negative charges, respectively. If they are prepared by filtration and assembly using ordinary solution blending, they will undergo positive and negative electrostatic reactions and precipitate during the solution blending process.

[0044] The addition of flame retardants further enhances the advantages of anisotropy in thermal management, providing a window of opportunity for the subsequent safety of the system even in the event of thermal defects in the material itself.

[0045] When exposed to flames or high temperatures, the HPCTP in the composite paper base decomposes to produce phosphorus-containing acids (such as H3PO4 or H4P2O7). This catalyzes the dehydration of the cellulose material in the condensed phase, forming a dense carbon layer that effectively blocks oxygen from the air. Simultaneously, the highly dense BNNS nanosheets and kaolin nanosheets act as a protective barrier and structural support, preventing heat and mass transfer between the gas and condensed phases through a tortuous effect. Therefore, the synergistic effect of HPCTP and BNNS nanolayers in the condensed phase further enhances its flame retardancy.

[0046] A halogen-free phosphorus-based flame retardant is used to construct an NP "condensed phase + gas phase" dual flame retardant mechanism.

[0047] In some embodiments, the loading of the BNNS layer and the kaolin nanolayer on the cellulose paper is 20-40%.

[0048] Too low a loading will result in poor thermal conductivity of the material; too high a loading will cause the nanosheets of the material to peel off easily, resulting in a decrease in mechanical properties.

[0049] In some embodiments, the kaolin nanolayer is a kaolin nanosheet.

[0050] In some embodiments, the size of a single nanosheet in the BNNS layer is 1µm-20µm; the size of a single nanosheet in the kaolin nanolayer is 1µm-20µm.

[0051] The sheet size refers to the extension scale (i.e., length and width) of sheet-like or layered materials in a two-dimensional plane. Its size directly affects the integrity of the heat conduction path. Larger sheet sizes make it easier to build a complete heat conduction network, but they also affect the orderliness of the structural arrangement. Smaller sheet sizes result in better material dispersion and greater stability in fabrication, but their size also limits the heat conduction path to some extent.

[0052] In some embodiments, the total number of BNNS layers and kaolin nanolayers is 40-80 layers.

[0053] If the number of nanosheets is too low, the material will have poor thermal conductivity; if the number of nanosheets is too high, the nanosheets will be easy to peel off, resulting in a decrease in mechanical properties.

[0054] In one embodiment of this application, a method for preparing anisotropic thermally conductive and flame-retardant battery cell spacers is proposed, comprising the following steps:

[0055] (1) The cellulose paper was alternately washed and dried in anhydrous ethanol and deionized water;

[0056] (2) The cellulose paper was soaked in BNNS solution to obtain a BNNS layer, and then dried to obtain a BNNS layer adsorbed by non-covalent bonding.

[0057] (3) The cellulose paper with the BNNS layer was impregnated with the kaolin nanosheet dispersion to obtain the kaolin nanolayer, and then dried to obtain the kaolin layer adsorbed by non-covalent bond interaction.

[0058] (4) Alternately repeat steps (2) and (3) to alternately coat the positively and negatively charged solutions until the required number of deposition cycles is reached, and a composite cellulose-based battery spacer is obtained.

[0059] In some embodiments, step (4) further includes a crosslinking step, in which the composite cellulose-based cell spacer is soaked in sodium tripolyphosphate for a period of time and then dried.

[0060] In some embodiments, the sodium tripolyphosphate soaking concentration is 1 mg / ml-10 mg / ml, and the soaking time is 1-12 hours.

[0061] If the concentration is too low, the polymerization effect is not obvious; if the concentration is too high, the polymerization will affect the mechanical properties of the material, and will also have a certain impact on the thermal conductivity.

[0062] In some embodiments, steps (2) and (3) are performed using layer-by-layer self-assembly (LBL) coating, wherein the single immersion time in LBL is 1 min to 10 min and the drying temperature is 40°C to 80°C. Preferably, the single immersion time is 2 min and the drying temperature is 60°C.

[0063] In terms of single soaking time, too short a time will result in the sample not being fully coated with the material. Excessively high drying temperatures can easily lead to dehydroxylation, which has a certain impact on its microstructure. Currently, the optimal drying temperature is 60℃.

[0064] In some embodiments, the concentration ratio of the BNNS solution to the kaolin nanosheet dispersion is 1:2-4:1.

[0065] An excessively high ratio will result in excessively high out-of-plane thermal conductivity, while the improvement in in-plane conductivity will be minimal, and it will also be detrimental to its anisotropy; an excessively low ratio will result in low in-plane thermal conductivity, which, while reducing out-of-plane thermal conductivity, will also be detrimental to its thermal conductivity applications. The optimal concentration ratio obtained is 1:1.

[0066] In some embodiments, the concentration of the BNNS solution is 1 mg / ml to 10 mg / ml; the concentration of the kaolin nanosheet dispersion is 1 mg / ml to 10 mg / ml.

[0067] In some embodiments, step (3) involves soaking the kaolin nanosheet dispersion to obtain a kaolin nanolayer and then washing it with ultrapure water.

[0068] Washing should be done to prevent sediment buildup on the material.

[0069] In some embodiments, the kaolin nanosheet dispersion is prepared by adding kaolin powder to deionized water after dispersing chitosan, followed by 1 hour of ultrasonication in a water bath and 2 hours of mechanical stirring to obtain the kaolin nanosheet dispersion.

[0070] Weigh the chitosan, add it to deionized water and stir to dissolve. While stirring, add glacial acetic acid dropwise to obtain deionized water with dispersed chitosan. Glacial acetic acid can promote the dissolution of chitosan; add 2-3 ml to 500 ml of chitosan solution.

[0071] In some embodiments, the preparation of the BNNS solution involves: ultrasonicating boron nitride nanosheets (BNNS) in 0.5 mg / ml-5 mg / ml sodium carboxymethyl cellulose in an ice bath for 1 hour to obtain a uniformly dispersed BNNS solution; adding a halogen-free phosphorus flame retardant to the obtained uniformly dispersed BNNS solution and polymerizing it for 6-24 hours; wherein the solid content of the halogen-free phosphorus flame retardant to BNNS is 2:1-1:4.

[0072] If the flame retardant content is too low or no flame retardant is added, the flame retardant performance of the material will be insignificant. Adding too much flame retardant will not linearly improve the flame retardant performance, but it will reduce the material's mechanical and thermal conductivity.

[0073] Before polymerization, the halogen-free phosphorus flame retardant needs to be dissolved in an alcohol solvent at 70-90℃ (preferably at 80℃) and then added dropwise to the BNNS dispersion and stirred overnight.

[0074] In some embodiments, the boron nitride nanosheets (BNNS) are prepared as follows: Hexagonal boron nitride powder (h-BN) is dispersed in a strongly alkaline alcohol-water mixture and hydrothermally treated at 160°C for 4 hours; the hydroxylated reaction solution is centrifuged and washed 3-6 times until the pH is below 9, and the supernatant is discarded; the precipitate after centrifugation is dispersed in a mixture of isopropanol and deionized water, and ultrasonically treated in a water bath for 4 hours to obtain the BNNS reaction solution; the reaction solution is centrifuged and dried to obtain BNNS nanosheets. The ratio of anhydrous ethanol to deionized water in the alcohol-water mixture is 135 ml:165 ml. The ratio of isopropanol to deionized water in the isopropanol-deionized water mixture is 1:1.

[0075] If BNNS that has been hydrothermally treated in a strongly alkaline solution is not washed down to a more neutral solution, it will have a certain impact on its subsequent use.

[0076] Example

[0077] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0078] In the following examples of this invention, some of the raw materials are as follows:

[0079] Hexagonal boron nitride (purity: 99.9%, Maclean's)

[0080] Kaolin (Purity: 98%, Shanlinshiyu Mineral Products Co., Ltd.)

[0081] Potassium hydroxide (analytical grade, Shanghai testing)

[0082] Sodium hydroxide (analytical grade, Shanghai testing)

[0083] Sodium tripolyphosphate (purity: 98%, Aladdin)

[0084] Carboxymethyl cellulose (Aladdin)

[0085] Chitosan (Aladdin)

[0086] In the following examples of this invention, the testing instruments are as follows:

[0087] The thermal conductivity was tested using a Netzsch LFA447 laser thermal conductivity meter, according to the standard ASTM E1461-2013.

[0088] Scanning electron microscopy analysis was performed using a Hitachi S-3500N scanning electron microscope in Japan.

[0089] Energy dispersive X-ray spectroscopy analysis was performed on an Oxford Instruments INCA instrument.

[0090] Example 1

[0091] Preparation:

[0092] (1) Preparation of hydroxylated boron nitride nanosheets

[0093] 19g of NaOH and 22.5g of KOH were dissolved in 165ml of ethanol and 135ml of aqueous solution. 6g of hexagonal boron nitride powder was added to this mixed solution, and the mixture was ultrasonically treated for 1 hour to disperse. The dispersed solution was placed in a hydrothermal reactor and reacted at 160℃ for 4 hours to obtain hydroxylated H-BN. The upper alkaline solution was removed by repeated centrifugation, yielding hydroxylated H-BN with pH < 9. The treated hydroxylated H-BN was then added to a 1:1 mixture of isopropanol and water, and ultrasonically exfoliated for 4 hours to obtain BNNS-OH.

[0094] (2) Preparation of boron nitride solution

[0095] Add 0.5g of sodium carboxymethyl cellulose to 500ml of deionized water and dissolve by stirring in an 80℃ water bath. Add 1g of hydroxylated boron nitride powder and sonicate for 1 hour to disperse. Weigh 1g of HPCTP powder, ensuring the powder is completely submerged in isopropanol. Stir the HPCTP solution in a 100℃ water bath until bubbles appear. Add the solution dropwise to the BNNS solution at a uniform and rapid rate while continuously stirring. After the solution is prepared, reduce the stirring speed to below 200 rpm and stir overnight.

[0096] (3) Preparation of Kaolin Nanosheet Dispersion

[0097] Weigh 0.5g of chitosan, add it to 400ml of deionized water and stir to dissolve. While stirring, add 1 drop of glacial acetic acid directly. Weigh 1g of kaolin nanosheets and disperse them in 100ml of deionized water. Stir the mixed solution.

[0098] (4) Preparation process of FBN-KL composite cell spacer

[0099] Cellulose paper was washed twice with ethanol and twice with ultrapure water, and then dried for later use. Based on the above-mentioned negatively charged boron nitride solution and positively charged chitosan / kaolin nanosheet solution, FBN-KL composite paper substrates were prepared using the LBL assembly method. In this case, cellulose paper was first placed on the prepared CMC / BNNS... - Immerse in HPCTP solution for 2 minutes, then dry in an oven at 70°C. The resulting product is treated with CMC / BNNS. - @HPCTP solution-coated cellulose paper immersed in kaolin @CS + Soak in solution for 2 minutes, then wash with ultrapure water and dry in a vacuum oven at 70°C. Repeat CMC / BNNS. - @HPCTP and Kaolin @CS + The solution coating process was repeated until 60 deposition cycles were achieved. The prepared battery cell spacer was then polymerized in a 5 mg / ml sodium tripolyphosphate solution at 60°C for 30 min to obtain anisotropic thermally conductive and flame-retardant battery cell spacer.

[0100] According to the laser thermal conductivity meter test, the in-plane thermal conductivity of the cell spacer is 5.52 W / (m·K), the out-of-plane thermal conductivity is 0.23 W / (m·K), the anisotropy coefficient is 24, the structure remains stable for 73s under extreme heat source test at 450℃, the operating temperature of the battery is reduced by 19.4% in the high-rate charging temperature control test of lithium battery, and the thermal runaway trigger test of single cell extends the thermal diffusion time from 34s in the blank group to 225s.

[0101] Example 2

[0102] Preparation work

[0103] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0104] The difference lies in the concentration of the kaolin solution, which is 1 mg / ml.

[0105] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 5.6 W / (m·K), the out-of-plane thermal conductivity is 0.39 W / (m·K), the anisotropy coefficient is 14.36, and the structure remains stable for 49s under extreme point heat source test at 450℃.

[0106] Example 3

[0107] Preparation work

[0108] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0109] The difference lies in the concentration of the kaolin solution, which is 4 mg / ml.

[0110] According to the laser thermal conductivity tester, the in-plane thermal conductivity of the cell spacer is 2.64 W / (m·K), the out-of-plane thermal conductivity is 0.21 W / (m·K), the anisotropy coefficient is 12.57, and the structure remains stable for 55s under extreme point heat source test at 450℃.

[0111] Example 4

[0112] Preparation work

[0113] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0114] The difference lies in the size of the hexagonal boron nitride nanosheets, which are 1 μm in size.

[0115] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 3.48 W / (m·K), the out-of-plane thermal conductivity is 0.22 W / (m·K), the anisotropy coefficient is 15.81, and the structure remains stable for 42s under extreme point heat source test at 450℃.

[0116] Example 5

[0117] Preparation work

[0118] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0119] The difference lies in the size of the hexagonal boron nitride nanosheets, which are 12 μm in size.

[0120] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 4.36 W / (m·K), the out-of-plane thermal conductivity is 0.23 W / (m·K), the anisotropy coefficient is 18.96, and the structure remains stable for 57s under extreme point heat source test at 450℃.

[0121] Example 6

[0122] Preparation work

[0123] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0124] The difference lies in the number of deposition cycles, which is 40 layers.

[0125] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 4.37 W / (m·K), the out-of-plane thermal conductivity is 0.44 W / (m·K), the anisotropy coefficient is 9.93, and the structure remains stable for 51 seconds under extreme point heat source test at 450℃.

[0126] Example 7

[0127] Preparation work

[0128] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0129] The difference lies in the number of deposition cycles, which is 80 layers.

[0130] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 4.47 W / (m·K), the out-of-plane thermal conductivity is 0.21 W / (m·K), the anisotropy coefficient is 21.28, and the structure remains stable for 67s under extreme point heat source test at 450℃.

[0131] Example 8

[0132] Preparation work

[0133] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0134] The difference lies in the sodium tripolyphosphate used for cross-linking, which is 10 mg / ml.

[0135] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 4.50 W / (m·K), the out-of-plane thermal conductivity is 0.24 W / (m·K), the anisotropy coefficient is 17.29, and the structure remains stable for 44s under extreme point heat source test at 450℃.

[0136] Example 9

[0137] Preparation work

[0138] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0139] The difference lies in the ratio of BNNS solids used in halogen-free phosphorus-based flame retardants: 1:2.

[0140] According to the laser thermal conductivity tester, the in-plane thermal conductivity of the cell spacer is 5.43 W / (m·K), the out-of-plane thermal conductivity is 0.24 W / (m·K), the anisotropy coefficient is 22.62, and the structure remains stable for 54s under extreme point heat source test at 450℃.

[0141] Example 10

[0142] Preparation work

[0143] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0144] The difference lies in the ratio of BNNS solids used in halogen-free phosphorus-based flame retardants: 2:1.

[0145] According to the laser thermal conductivity tester, the in-plane thermal conductivity of the cell spacer is 4.47 W / (m·K), the out-of-plane thermal conductivity is 0.22 W / (m·K), the anisotropy coefficient is 20.32, and the structure remains stable for 47s under extreme point heat source test at 450℃.

[0146] Comparative Example 1

[0147] Preparation work

[0148] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0149] The difference lies in step (4), where the cellulose paper is only first applied to the prepared CMC / BNNS. - Soak in HPCTP solution for 2 minutes, then dry in an oven at 70°C. Do not soak kaolin in CS solution again. + Solution.

[0150] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 3.53 W / (m·K), the out-of-plane thermal conductivity is 0.48 W / (m·K), the anisotropy coefficient is 5.27, and the structure remains stable for 39s under extreme point heat source test at 450℃.

[0151] Comparative Example 2

[0152] Preparation work

[0153] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0154] The difference lies in step (4), where the cellulose paper is only first applied to the prepared kaolin @CS + Soak in the solution for 2 minutes, then dry in an oven at 70°C. Do not soak again in CMC / BNNS. - @HPCTP solution.

[0155] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 1.36 W / (m·K), the out-of-plane thermal conductivity is 0.12 W / (m·K), the anisotropy coefficient is 11.33, and the structure remains stable for 10s under extreme point heat source test at 450℃.

[0156] Comparative Example 3

[0157] Preparation work

[0158] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0159] The difference lies in the fact that it is used without the cross-linking treatment of sodium tripolyphosphate.

[0160] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 4.07 W / (m·K), the out-of-plane thermal conductivity is 0.27 W / (m·K), the anisotropy coefficient is 15.07, and the structure remains stable for 41s under extreme point heat source test at 450℃.

[0161] Comparative Example 4

[0162] Preparation work

[0163] The raw materials and preparation process in this embodiment are the same as in Embodiment 1.

[0164] The difference lies in whether or not HPCTP is used for modification.

[0165] According to the test of the laser thermal conductivity meter, the in-plane thermal conductivity of the cell spacer is 4.17 W / (m·K), the out-of-plane thermal conductivity is 0.41 W / (m·K), the anisotropy coefficient is 10.17, and the structure remains stable for 21 seconds under extreme point heat source test at 450℃.

[0166] Table 1 shows the thermal defect time and... Figure 2 Thermal conductivity and mechanical properties of 3.

[0167]

[0168] from Figure 1 As can be clearly seen in image a, the spacers of this battery cell have a distinct layered stacked structure. Figure 1 As shown in b, the nanosheets of this material effectively adhere to the fiber, forming a thermally conductive pathway, and the structure remains intact. This leads to the deduction of the anisotropic mechanism of this invention, as well as the effectiveness of the BNNS modification and layer-by-layer assembly design.

[0169] As in Example 1 Figure 2 As shown, the anisotropic two-dimensional thermally conductive boron nitride nanosheets are located in the in-plane direction and are oriented horizontally to construct continuous thermal conductivity pathways, thus resulting in high in-plane thermal conductivity of the prepared material. However, the kaolin nanosheets are stacked out-of-plane, blocking out-of-plane thermal conductivity pathways, thus resulting in low out-of-plane thermal conductivity of the prepared material.

[0170] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An anisotropic thermally conductive and flame-retardant battery cell spacer, characterized in that, The battery consists of BNNS layers and kaolin nanolayers that are self-assembled and alternately stacked on cellulose paper. The BNNS nanosheets on the BNNS layers are polymerized with hexaphenoxycyclotriphosphazene flame retardant through π-π conjugation, forming a composite cellulose-based battery cell spacer. The phosphorus-containing acid produced by the thermal decomposition of the hexaphenoxycyclotriphosphazene flame retardant can catalyze the dehydration of the cellulose paper in the condensed phase to form a dense carbon layer, which effectively blocks oxygen in the air. The dense BNNS nanosheets and kaolin nanosheets play the role of protective barrier and structural support. The loading of the BNNS layer and kaolin nanolayer on the cellulose paper is 10-40%; the total number of the BNNS layer and kaolin nanolayer is 40-80 layers. The spacer is obtained by the following method: (1) The cellulose paper was alternately washed and dried in anhydrous ethanol and deionized water; (2) The cellulose paper was soaked in BNNS solution to obtain a BNNS layer, and then dried to obtain a BNNS layer adsorbed by non-covalent bonding. (3) The cellulose paper with the BNNS layer was impregnated with the kaolin nanosheet dispersion to obtain the kaolin nanolayer, and then dried to obtain the kaolin layer adsorbed by non-covalent bond interaction. (4) Alternately repeat steps (2) and (3) to alternately coat the positively and negatively charged solutions until the required number of deposition cycles is reached, and a composite cellulose-based battery cell spacer is obtained; Preparation of the kaolin nanosheet dispersion: Kaolin powder was added to deionized water after dispersing chitosan, and the mixture was subjected to ultrasonication in a water bath for 1 hour and mechanical stirring for 2 hours to obtain the kaolin nanosheet dispersion. Preparation of the BNNS solution: Boron nitride nanosheets were ultrasonically dissolved in 0.5 mg / ml-5 mg / ml sodium carboxymethyl cellulose in an ice bath for 1 hour to obtain a uniformly dispersed BNNS solution; hexaphenoxycyclotriphosphazene flame retardant was added to the obtained uniformly dispersed BNNS solution, and polymerization was carried out for 6-24 hours. Preparation of the boron nitride nanosheets: Hexagonal boron nitride powder was dispersed in a strongly alkaline alcohol-water mixed solution and hydrothermally treated at 160°C for 4 hours; the hydroxylated reaction solution was centrifuged and washed 3-6 times until the pH was below 9, and the supernatant was discarded; the precipitate after centrifugation was dispersed in a mixed solution of isopropanol and deionized water, and ultrasonically treated in a water bath for 4 hours to obtain the BNNS reaction solution; the reaction solution was centrifuged and dried to obtain BNNS nanosheets; wherein, the ratio of anhydrous ethanol to deionized water in the alcohol-water mixed solution was 135 ml: 165 ml, and the ratio of isopropanol to deionized water in the mixed solution of isopropanol and deionized water was 1:

1.

2. The anisotropic thermally conductive and flame-retardant battery cell spacer according to claim 1, characterized in that, The size of a single nanosheet in the BNNS layer is 1μm-20μm; the size of a single nanosheet in the kaolin nanolayer is 1μm-20μm.

3. The anisotropic thermally conductive and flame-retardant battery cell spacer according to claim 1, characterized in that, Step (4) further includes a crosslinking step, in which the composite cellulose-based battery cell spacer is soaked in sodium tripolyphosphate at a concentration of 1 mg / ml-10 mg / ml for 1-12 hours and then dried.

4. The anisotropic thermally conductive and flame-retardant battery cell spacer according to claim 1, characterized in that, The coating process in steps (2) and (3) is carried out by layer-by-layer self-assembly, wherein the single immersion time in the layer-by-layer self-assembly is 1 min-10 min and the drying temperature is 40℃-80℃.

5. The anisotropic thermally conductive and flame-retardant battery cell spacer according to claim 1, characterized in that, The concentration of the BNNS solution is 1 mg / ml-10 mg / ml; the concentration of the kaolin nanosheet dispersion is 1 mg / ml-10 mg / ml; and the concentration ratio of the BNNS solution to the kaolin nanosheet dispersion is (0.5-4):1.

Images