Method for improving hydrogen desorption performance of lithium borohydride by co-doping fluoride and MXene

Abstract

The invention relates to a method for improving hydrogen desorption performance of lithium borohydride by co-doping fluoride and MXene. The provided composite hydrogen storage material comprises the following raw material components in parts by weight: 50-80 wt% of LiBH4, 10-25 wt% of Ti3C2 MXene and 10-25 wt% of metal fluoride. Compared with the prior art, the metal fluoride and the Ti3C2 MXene material are introduced into the LiBH4 hydrogen storage material through a simple and efficient ball milling process, the hydrogen desorption temperature of LiBH4 is effectively reduced through the synergistic effect of the metal fluoride and the Ti3C2 MXene material, meanwhile, the hydrogen desorption capacity of LiBH4 is improved, the prepared compound can achieve hydrogen desorption at about 78.70 DEG C, the peak hydrogen desorption temperature of the compound is about 344.25 DEG C, and the hydrogen desorption efficiency is greatly improved. And finally, 11.46 wt% of hydrogen and the like are released at the temperature of 400 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen storage materials technology, and relates to a lithium borohydride-based composite hydrogen storage material co-doped with fluoride and MXene and its preparation method. Background Technology

[0002] Lithium borohydride (LiBH4) has attracted widespread attention as an excellent hydrogen storage material due to its extremely high hydrogen storage capacity (LiBH4: 18.5 wt%; Mg(BH4)2: 14.8 wt%; Ca(BH4)2: 11.6 wt%). However, LiBH4 only begins to release hydrogen above 300 °C, with the main hydrogen release process occurring around 400 °C. Moreover, the hydrogen release products LiH and B from pure LiBH4 require very harsh conditions to achieve hydrogenation, such as hydrogen absorption at 600 °C and 35 MPa hydrogen pressure. The poor thermodynamic and kinetic properties of LiBH4, along with its low reversibility, severely limit its development.

[0003] Commonly used methods for modifying LiBH4 for hydrogen storage include adding catalysts, nano-confining, and forming composite systems with other hydrogen storage materials. For example, a related report (Improving the hydrogen storage performance of lithiumborohydride by Ti3C2 MXene, International Journal of Hydrogen Energy, 5 44(2019) 29297-29303) describes the preparation of LiBH4- using a ball milling method. x The Ti3C2 composite, in which LiBH4-40 wt% Ti3C2 exhibits initial and peak hydrogen release temperatures of 120 and 408 °C, respectively, which are 180 and 80 °C lower than those of pure LiBH4. It can release 5.37 wt% hydrogen gas within 1 hour at 350 °C, while LiBH4 releases only 0.5 wt% hydrogen gas under the same conditions. Furthermore, a related report (Synergetic action of 0D / 2D / 3D N-doped carbon nanocages and NbB2 nanocatalyst on reversible hydrogen storage performance of lithiumborohydride, Chemical Engineering Journal, 485 (2024) 150090) utilizes nitrogen-doped carbon nanocages to confine metal fluorides NbF5 and LiBH4 to prepare... xLBH@NC-NbF5 composite. Among them, 50LBH@NC-NbF5 composite can start to release hydrogen at 140℃, and release 7.55wt% of hydrogen within 39min in isothermal hydrogen release test at 320℃. The cycle test at 300℃ shows that the composite still maintains 93% of hydrogen release capacity after 20 cycles. Although the above-mentioned catalyst has significantly improved the hydrogen release performance of LiBH4, the resulting composite hydrogen storage system still has the problem of high hydrogen release temperature, with the initial hydrogen release temperature higher than 100℃ and the fastest hydrogen release rate reached at about 400℃. In addition, although the confinement of carbon material can effectively reduce the peak hydrogen release temperature, the low loading amount of the carbon material leads to a significant reduction in the effective hydrogen release capacity of the hydrogen storage system. SUMMARY

[0004] The purpose of the present application is to provide a fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material and a preparation method thereof, so as to reduce the thermodynamic stability of lithium borohydride hydrogen storage material and improve its hydrogen release capacity and hydrogen release kinetics.

[0005] The purpose of the present application can be achieved by the following technical solutions: In one aspect, the present application provides a fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material, which comprises the following raw material components by weight: LiBH450-80 wt%, Ti3C2 MXene 10-25 wt%, and metal fluoride 10-25 wt%.

[0006] Further, the Ti3C2 MXene is prepared by the following steps: S1, dissolving lithium fluoride in a hydrochloric acid solution, stirring uniformly to obtain an etching solution; S2, adding titanium aluminum carbide to the etching solution in S1, removing the aluminum layer after mixing, obtaining a mixed solution, then centrifuging at room temperature, separating the supernatant to obtain a sticky precipitate; S3, dispersing the sticky precipitate into deionized water and ultrasonic treating under inert atmosphere, then continuing to centrifuge at room temperature, collecting the upper liquid, and finally freeze-drying to obtain Ti3C2 MXene material.

[0007] Further, in S1, the hydrochloric acid solution is mixed by concentrated hydrochloric acid and water in a volume ratio of (30-35):(10-15), and the mass fraction of the concentrated hydrochloric acid is 36-38%.

[0008] Further, in S2, the process of removing the aluminum layer by mixing is as follows: treating at 35-45℃ for 20-28h.

[0009] Further, in S2, the centrifugal process is: centrifugation at 8000-10000 rpm for 10-20 min, repeated several times until sticky precipitate appears, and the PH of the upper liquid is 6-7.

[0010] Further, in S3, the ultrasonic treatment time is 2-3 h, and here, the temperature during ultrasonic treatment should not be too high, and the treatment can be performed in flowing water. The centrifugal process in S3 is: centrifugation at 3000-4000 rpm for 40-80 min.

[0011] Further, in S3, the freeze-drying process is: after the equipment is cooled to-50 °C and kept for 1 h, the sample is put in, vacuumized to <60 Pa, and freeze-drying is started, and the freeze-drying time is about 24 h.

[0012] Further, the metal fluoride can be directly commercially available, and examples can be K2NbF7, K2TiF6, K2SiF6 or NbF5. In addition, the purity is generally controlled to be ≥95%.

[0013] In another aspect, the application provides a preparation method of a fluorine and MXene co-doped lithium borohydride-based composite hydrogen storage material, which comprises the following steps: uniformly mixing LiBH4, Ti3C2 MXene and metal fluoride, loading into a ball mill jar, and performing ball milling treatment to obtain the fluorine and MXene co-doped lithium borohydride-based composite hydrogen storage material.

[0014] Further, in the ball milling process, the ball-to-material ratio is 80-100:1.

[0015] Further, the ball milling process is specifically: the ball milling speed is controlled to be 400-500 rpm, and the time is 15-180 min. When the ball milling time is relatively long, 5 min of rest is controlled every 30 min.

[0016] Compared with the prior art, the application has the following advantages: (1) The application provides a simple and efficient method for introducing metal / non-metal fluoride and Ti3C2 MXene into LiBH4 hydrogen storage material, and the synergistic catalytic effect of the two is used to improve the hydrogen release performance thereof; (2) The prepared LiBH4-based composite hydrogen storage material has excellent hydrogen release performance, can realize hydrogen release starting at about 78.70 °C, the peak hydrogen release temperature is about 344.25 °C, and finally 11.46 wt% of hydrogen gas is released at 400 °C; (3) The metal / non-metal fluoride and Ti3C2 MXene co-doped catalyst generates KF, NbB2, Li3BO3 and elemental metal Ti active substances through ball milling and hydrogen release process, which collectively promote the dehydrogenation reaction of LiBH4. KF acts as an active site to promote the dehydrogenation process of LiBH4, and NbB2, Li3BO3 and elemental metal Ti weaken the Li-B and B-H bond strength in LiBH4 to accelerate the dehydrogenation process. + -[BH4] - and B-H bond strength to accelerate the dehydrogenation process. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 XRD patterns of multilayer and few-layer Ti3C2 MXene and SEM image of few-layer Ti3C2 MXene of Example 1 of the present application.

[0018] Figure 2 XRD pattern of LiBH4-20Ti3C2 / 20K2NbF7 of Example 1 of the present application.

[0019] Figure 3 SEM image of LiBH4-20Ti3C2 / 20K2NbF7 of Example 1 of the present application.

[0020] Figure 4 Temperature programmed desorption curve of LiBH4-20Ti3C2 / 20K2NbF7 of Example 1 of the present application.

[0021] Figure 5 Temperature programmed desorption curves of LiBH4-20Ti3C2 / 20K2NbF7 ball milled for 15 min and 180 min, respectively, in Example 2 of the present application.

[0022] Figure 6 Temperature programmed desorption curve of LiBH4-20Ti3C2 / 20NbF5 in Example 3 of the present application.

[0023] Figure 7 Temperature programmed desorption curve of LiBH4-20Ti3C2 / 20K2TiF6 in Example 4 of the present application.

[0024] Figure 8 Temperature programmed desorption curve of LiBH4-40K2NbF7 in Comparative Example 1 of the present application.

[0025] Figure 9 Temperature programmed desorption curve of LiBH4-40Ti3C2 in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0026] The application will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments are implemented on the premise of the technical solutions of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing specific embodiments only and is not intended to be limiting of the application.

[0028] The selection scope of the terms "and / or", "or / and", "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, including any two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", "and / or", it should be understood that in this application, the technical solution undoubtedly includes the technical solution connected by "logical and", and also undoubtedly includes the technical solution connected by "logical or".

[0029] In this application, the technical features described in an open manner include a closed technical solution composed of listed features, and also include an open technical solution containing listed features.

[0030] In this application, when referring to a numerical interval, unless otherwise specified, the numerical interval is considered to be continuous, and includes the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0031] Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value can itself be combined with any other point or single numerical value as a lower limit or an upper limit to form a range not explicitly recited.

[0032] The temperature parameters in the present application, if not particularly limited, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for fluctuations within the accuracy range of instrument control. Fluctuations within a range of, for example, ±5°C, ±4°C, ±3°C, ±2°C, ±1°C are allowed.

[0033] In the present application, "suitable", "suitable manner", "any suitable manner", and the like, are used in the sense of enabling the technical solutions of the present application, solving the technical problems of the present application, and achieving the intended technical effects of the present application.

[0034] In the present application, "further", "still further", "in particular", and the like are used for the purpose of description, and do not mean that the content is different, but should not be understood as limiting the scope of protection of the present application.

[0035] In the present application, "optionally", "optional", and "optional" mean that it can or can not be present, i.e., it means that it is selected from either of the two parallel schemes "has" or "has not". If there are multiple "optionally" in a technical solution, and there is no special description, and there is no contradictory relationship or mutual restriction, each "optionally" is independent.

[0036] In the description of the application, "multiple" means at least two, for example, two, three, and the like, unless otherwise specified.

[0037] Unless otherwise specified, all formulations and tests in the present application occur in an environment of 25°C.

[0038] In the present application, "include", "contain", "comprise", "have", or other variants are intended to cover non-closed inclusion, and there is no distinction between these terms. The term "comprise" means that other steps and ingredients can be added without affecting the final result. The compositions and methods / processes of the present application comprise, consist of, and consist essentially of the essential elements and limitations described herein, and any additional or optional ingredients, components, steps, or limitations described herein. There is no distinction between the terms "efficiency", "performance", "effect", and "efficacy" in the present application.

[0039] If not specifically stated, all embodiments and optional embodiments of the present application can be combined to form new technical solutions. If not specifically stated, all technical features and optional technical features of the present application can be combined to form new technical solutions.

[0040] If not specifically stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence.

[0041] In the following examples, the metal fluoride used is purchased from Alfa Aesar Chemical Co., Ltd., with a purity of ≥95%; the titanium aluminum carbide used is purchased from Xinyan Technology Co., Ltd.

[0042] Example 1 The Ti3C2 MXene and K2NbF7 catalyst for improving the hydrogen release performance of lithium borohydride provided in this example is prepared by the following method: The first step is the preparation method of the Ti3C2 MXene catalyst, which comprises the following steps: (1) 2 g of lithium fluoride is dissolved in 30 mL of concentrated hydrochloric acid (mass fraction of 37%) and 10 mL of deionized water, and fully stirred to obtain an etching solution; (2) 2 g of titanium aluminum carbide (Ti3AlC2) is slowly added to the etching solution, and after mixing at a temperature of 35 °C for 24 hours to remove the aluminum layer, a mixed solution is obtained; (3) The mixed solution is centrifuged at a speed of 8500 rpm for 15 min at room temperature, repeated 7-8 times until a sticky precipitate appears, the PH of the upper liquid is 6-7, and the sticky precipitate is obtained by removing the upper liquid; (4) The sticky precipitate is dispersed in an appropriate amount of deionized water, and ultrasonic treatment is carried out for 120 min under an argon atmosphere.

[0043] (5) After the completion of ultrasonic treatment, the upper liquid is collected after centrifugation at a speed of 3500 rpm for 60 min at room temperature; (6) The collected upper liquid is freeze-dried for 20 h to obtain a few-layer Ti3C2 MXene material.

[0044] The second step is to manually mix LiBH4, Ti3C2 MXene and K2NbF7 materials in a glove box according to a mass percentage of 3:1:1 and load them into a ball mill jar for ball milling treatment to obtain a Ti3C2 MXene and K2NbF7 co-doped LiBH4 composite hydrogen storage material, and the ball milling parameters are as follows: ball milling speed is 400 rpm, time is 30 min, and ball-to-material ratio is 80:1.

[0045] The prepared composite material is marked as LiBH4-20Ti3C2 / 20K2NbF7, which can release hydrogen at about 78.70 °C, reach a peak hydrogen release temperature at 344.25 °C, and finally release 11.46 wt% of hydrogen at 400 °C.

[0046] Figure 1In the figure, (a) shows the XRD patterns of multilayer and few-layer Ti3C2 MXene, and (b) shows the SEM images of few-layer Ti3C2 MXene. To ensure the successful preparation of monolayer Ti3C2 MXene, the XRD patterns of multilayer (denoted as M-Ti3C2 MXene) and monolayer Ti3C2 MXene (denoted as Ti3C2 MXene) were compared. M-Ti3C2 MXene was obtained by vacuum drying of the viscous precipitate obtained in step S2. As shown in Figure (a), the (0 0 2) crystal planes of M-Ti3C2 and Ti3C2 MXene are located at 2θ ≈ 8.48 and 6.90°, respectively, indicating that the interplanar spacing of monolayer Ti3C2 MXene is greater than that of M-Ti3C2 MXene, thus successfully preparing monolayer Ti3C2 MXene. As can be seen from Figure (b), the prepared few-layer Ti3C2MXene exhibits an ultrathin layered structure, indicating that the few-layer Ti3C2MXene was successfully prepared.

[0047] Figure 2 The image shows the XRD pattern of the LiBH4-20Ti3C2 / 20K2NbF7 composite hydrogen storage material. As can be seen from the image, only LiBH4 and the newly generated LiF from Ti3C2 were detected in the composite material, while the peak of K2NbF7 disappeared completely. This may be because K2NbF7 and LiBH4 reacted during the ball milling process to generate LiF and a new phase containing Nb. However, due to the poor crystallinity of the new phase, it could not be detected by XRD.

[0048] Figure 3 The image shows a SEM image of the LiBH4-20Ti3C2 / 20K2NbF7 composite hydrogen storage material. As shown, after a short ball milling time of 30 minutes, the material particles were significantly refined and well dispersed. This is because K2NbF7 has high hardness, which helps to refine the particles. Meanwhile, Ti3C2 MXene acts as a grinding aid and dispersant, improving ball milling efficiency and inhibiting particle agglomeration to some extent.

[0049] Figure 4 The figure shows the temperature-programmed desorption curve of the LiBH4-20Ti3C2 / 20K2NbF7 composite hydrogen storage material, heated from room temperature to 500 °C at a rate of 2 °C / min. As shown in the figure, pure LiBH4 begins to release hydrogen at 312.13 °C, with a peak hydrogen release temperature of approximately 457.93 °C. Heating to 500 °C releases 9.23 wt% hydrogen. In contrast, the LiBH4-20Ti3C2 / 20K2NbF7 composite hydrogen storage material has initial and peak hydrogen release temperatures of 78.70 °C and 344.25 °C, respectively, which are 233.36 and 113.68 °C lower than those of pure LiBH4. It finally releases 11.46 wt% hydrogen at 400 °C.

[0050] Example 2 The difference from Example 1 is that the ball milling parameters in the second step are as follows: the ball milling speed is 400 rpm, the time is 15 min and 180 min respectively, and the ball-to-material ratio is 80:1.

[0051] Figure 5 The temperature-programmed desorption curves of the LiBH4-20Ti3C2 / 20K2NbF7 composite hydrogen storage material after ball milling for 15 min and 180 min are shown in the figure. As shown in the figure, the composite material prepared by ball milling for 15 min exhibits better hydrogen desorption performance, starting to desorb hydrogen at approximately 150 °C, reaching a peak hydrogen desorption temperature of 353.69 °C, and finally releasing 12.15 wt% hydrogen gas at 500 °C. Compared with Example 1, the hydrogen desorption of the sample in Example 2 is significantly higher. The reason for this is that the ball milling time of the sample in Example 2 was shorter, resulting in insufficient mixing or insufficient particle refinement, leading to insufficient contact between the main material LiBH4 and the catalyst, and the catalyst could not fully exert its catalytic effect.

[0052] Furthermore, because Ti3C2 MXene and K2NbF7 have high ball milling efficiency, with Ti3C2 MXene and K2NbF7 acting as grinding aid and dispersant respectively, short-time ball milling can effectively reduce particle size, ensuring complete and uniform mixing of LiBH4, Ti3C2 MXene, and K2NbF7. Therefore, excessively long ball milling times (e.g., 180 minutes) can lead to over-refinement of particles and agglomeration, causing some LiBH4 to be encapsulated. This prevents Ti3C2 MXene and K2NbF7 from fully exerting their catalytic performance, ultimately resulting in a decrease in hydrogen storage capacity.

[0053] Example 3 The difference from Example 1 is that the metal fluoride in the second step is NbF5, and the resulting composite hydrogen storage material is LiBH4-20Ti3C2 / 20NbF5.

[0054] Figure 6 The temperature-programmed desorption curve of the LiBH4-20Ti3C2 / 20NbF5 composite hydrogen storage material is shown in the figure. The peak hydrogen release temperature of the composite material is about 345.14 ℃, and the main hydrogen release process ends at about 390.46 ℃. Finally, the temperature is raised to 500 ℃ to release 10.43 wt% hydrogen.

[0055] As can be seen, compared with Example 3, Example 1, which uses K2NbF7 as a metal fluoride to construct hydrogen storage material, has obvious advantages in hydrogen release temperature, hydrogen release capacity and hydrogen release kinetics.

[0056] Example 4 The difference from Example 1 is that the metal fluoride in the second step is K2TiF6, and LiBH4-20Ti3C2 / 20K2TiF6 composite hydrogen storage material is prepared.

[0057] Figure 7 The temperature-programmed desorption curve of the LiBH4-20Ti3C2 / 20K2TiF6 composite hydrogen storage material is shown in the figure. The composite material begins to release hydrogen at 88.96 °C, then undergoes a rapid hydrogen release process, and finally releases 12.74 wt% hydrogen when the temperature is raised to 500 °C.

[0058] Example 1 and Example 4 have similar hydrogen desorption performance, which may be because both are co-doped with Ti3C2 MXene and bimetallic fluoride, further demonstrating that the synergistic effect between Ti3C2 MXene and bimetallic fluoride can effectively improve the hydrogen desorption performance of LiBH4.

[0059] Comparative Example 1: Compared with Example 1, most of them are the same, except that in the second step, 20 wt% of Ti3C2 MXene is replaced with an equal amount of K2NbF7, that is, the weight ratio of LiBH4 to K2NbF7 is 6:4.

[0060] Figure 8 The figure shows the temperature-programmed desorption curve of the LiBH4-40K2NbF7 composite material, heated from room temperature to 500 °C at a rate of 2 °C / min. As shown, the LiBH4-40K2NbF7 composite material begins to release hydrogen at 88.99 °C, reaches a peak hydrogen release rate at around 350.02 °C, and finally releases 10.25 wt% hydrogen gas when the temperature is raised to 500 °C.

[0061] Compared with Comparative Example 1, the initial hydrogen release temperature and peak hydrogen release temperature of Example 1 decreased by 10.29 °C and 5.95 °C, respectively. Further heating to 500 °C significantly improved the hydrogen release capacity of Example 1 compared to Comparative Example 1, increasing from 10.25 wt% to 12.24 wt%.

[0062] Comparative Example 2: The majority of the contents are the same as in Example 1, except that in the second step, 20 wt% of K2NbF7 is replaced with an equal amount of Ti3C2 MXene, i.e., the weight ratio of LiBH4 to Ti3C2 MXene is 6:4.

[0063] Figure 9The figure shows the temperature-programmed desorption curve of the LiBH4-40Ti3C2 composite material, heated from room temperature to 500 °C at a rate of 2 °C / min. As shown, the initial and peak hydrogen release temperatures are 165.52 °C and 304.96 °C, respectively, and 9.54 wt% hydrogen is finally released at 500 °C.

[0064] Compared with Comparative Example 2, Example 1 has a lower initial hydrogen release temperature and a higher hydrogen release capacity. Its initial hydrogen release temperature decreased by 86.82 °C and its hydrogen release capacity at 500 °C increased by 2.7 wt%.

[0065] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material, characterized in that, The raw material components include the following weight parts: LiBH450~80 wt%, Ti3C2 MXene 10~25 wt%, and metal fluoride 10~25 wt%.

2. The fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material according to claim 1, characterized in that, The Ti3C2 MXene is prepared by the following steps: S1, dissolving lithium fluoride in a hydrochloric acid solution, stirring uniformly to obtain an etching solution; S2, adding titanium aluminum carbide to the etching solution in S1, removing the aluminum layer after mixing, obtaining a mixed solution, then centrifuging at room temperature, separating the supernatant, obtaining a sticky precipitate; S3, dispersing the sticky precipitate into deionized water and ultrasonic treatment under an inert atmosphere, then continuing to centrifuge at room temperature, collecting the upper liquid, and finally freeze-drying to obtain a Ti3C2 MXene material.

3. The fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material according to claim 2, characterized in that, In S1, the hydrochloric acid solution is mixed by concentrated hydrochloric acid and water in a volume ratio of (30~35):(10~15), and the mass fraction of the concentrated hydrochloric acid is 36~38%.

4. The fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material of claim 2, wherein, In S2, the process of removing the aluminum layer by mixing is: treating at 35~45℃ for 20~28h.

5. The fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material according to claim 2, characterized in that, In S2, the centrifugation process is: centrifuging at a speed of 8000~10000 rpm for 10~20 min, repeating several times until a sticky precipitate appears, and the PH of the upper liquid is 6~7.

6. The fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material according to claim 2, characterized in that, In S3, the ultrasonic treatment time is 2~3h; The centrifugation process in S3 is: centrifuging at a speed of 3000~4000 rpm for 40~80 min.

7. The fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material according to claim 1, characterized in that, The metal fluoride is K2NbF7, K2TiF6, K2SiF6, or NbF5.

8. The preparation method of a fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material according to any one of claims 1-7, characterized in that, After mixing LiBH4, Ti3C2 MXene, and metal fluoride uniformly, they are loaded into a ball mill tank for ball milling treatment to obtain a fluoride and MXene co-doped lithium borohydride-based composite hydrogen storage material.

9. The method according to claim 8, wherein the method is characterized by, During ball milling, the ball-to-material ratio is 80~100:1; The ball milling process is: controlling the ball milling speed to be 400~500 rpm for 15~180 min.

10. A method for improving the hydrogen release performance of lithium borohydride by co-doping fluorides and MXenes, characterized in that, According to the ratio of LiBH450~80 wt%, Ti3C2 MXene 10~25 wt%, and metal fluoride 10~25 wt%, the metal fluoride, Ti3C2 MXene, and LiBH4 are co-doped to obtain a lithium borohydride-based composite hydrogen storage material with significantly improved hydrogen release performance.

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