Alkali metal-MOF carbon-based composite anode and alkali metal battery thereof

Abstract

The invention discloses an alkali metal-MOF carbon-based composite anode and an alkali metal battery thereof, which are characterized in that an MOF-derived hollow carbon skeleton and an adhesive are mixed and pulpified to serve as an active layer, the active layer is coated on a metal current collector, and then alkali metal is filled in the active layer to prepare the alkali metal-MOF carbon-based composite anode. The preparation process of the MOF-derived hollow carbon skeleton specifically comprises the following steps: firstly, adding an MOF material into methanol, then carrying out ultrasonic oscillation dissolution, and then adding phytic acid for etching to obtain a hollow carbon skeleton precursor; and finally carbonizing the hollow carbon skeleton precursor to obtain the MOF-derived hollow carbon skeleton. The alkali metal-MOF carbon-based composite anode with high alkali metal loading capacity, high energy density and high performance is prepared by loading the alkali metal through the MOF derived hollow carbon skeleton, so that the nonuniformity of deposited alkali metal in the circulation process under large current is improved, the volume effect and interface side reaction are reduced, and the coulombic efficiency and the circulation stability of an alkali metal battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of alkali metal battery technology, specifically relating to an alkali metal-MOF carbon-based composite anode and its alkali metal battery. Background Technology

[0002] With the development of long-range electric vehicles and energy storage devices, the demand for batteries with high energy density and long cycle life is increasing. However, lithium-ion batteries are limited by the theoretical capacity of graphite cathodes, making it difficult to break through 300 Wh / kg in energy density. Alkali metal anodes have high theoretical specific capacity and low electrochemical potential, and can be matched with cathodes with high theoretical specific capacity such as S and O2 to construct high-energy-density metal batteries such as Li / Na / KS, Li / Na / KI, and Li / Na / K-O2, thereby meeting the requirements of advanced energy storage technologies. The alkali metals mentioned are mainly Li, Na, and K, among which Li has the lowest electrochemical potential (−3.04 V) and extremely high theoretical specific capacity (3860 mAh / g). Although the theoretical specific capacity of Na and K is not as high as that of Li, Na and K are abundant and inexpensive, which still attracts great interest from researchers.

[0003] However, due to the lack of a framework in alkali metals, a huge volume effect is generated during charge-discharge cycles, causing the SEI film to be continuously damaged and repaired, making it difficult to maintain a stable solid-liquid interface. On the other hand, the unevenness of the alkali metal anode surface causes abnormal distribution of alkali metal cations and electrons at the interface, making it difficult for alkali metals to be uniformly deposited on the anode surface, resulting in a large amount of dendrite growth and accumulation, which inevitably leads to a reduction in coulombic efficiency, a sharp decrease in cycle performance, and huge safety hazards.

[0004] The most critical reason for the numerous problems with alkali metal batteries is that the alkali metal anode comes into direct contact with the electrolyte in the battery. Alkali metals have extremely high reactivity, and they will react with even organic electrolytes, resulting in numerous side reactions, huge volume effects, repeated damage and repair of the SEI film, dendrite growth followed by fracture, instability of the solid-liquid interface, and reduced coulombic efficiency. Currently, various hollow lithium-loving carbon frameworks have been extensively studied. For example, Fei-HuDu et al. [Li SQ, Zhang L, Liu TT, et al. A dendrite-free lithium-metal anodeenabled by designed ultrathin MgF2 nanosheets encapsulated inside nitrogen-doped graphene-like hollow nanospheres[J]. Advanced Materials, 2022, 34(24):2201801.] prepared graphene-like hollow nanospheres with ultrathin MgF2 nanosheets encapsulated inside. The ultrathin MgF2 nanosheets attached to the inner wall of the graphene-like hollow nanospheres serve as the inducing core for lithium deposition, achieving selective encapsulation of lithium metal, constraining the growth of lithium dendrites, inhibiting the occurrence of lithium dendrites and dead lithium, reducing unnecessary electrolyte consumption, and promoting stable SEI formation. Jingze Li et al. [Song, Z., Liu, Y., Wang, Z. et al. Synergistic modulation of Li nucleation / growth enabled by CNTs-wrapped lithiophilic CoP / Co2P-decorated hollow carbon polyhedron host for stable lithium metal anodes. NanoRes. 16, 4961–4969 (2023).] demonstrated that by depositing lithium metal into MOF-derived nitrogen-doped porous polyhedral carbon materials uniformly encapsulated with CoP / CoP2 nanoparticles, lithium metal was selectively induced to deposit within a small number of pores that appeared after carbonization, and was stably encapsulated, thus obtaining a stable 3D lithium metal anode, effectively mitigating the volume effect and ensuring uniform lithium deposition. Although current research has made great progress, such closed lithiophilic 3D hollow carbon frameworks can effectively induce alkali metal deposition into their hollow internal structure, but most of these materials have low yields, complex preparation processes, and high costs, thus preventing large-scale production. Meanwhile, MOF-derived carbon skeletons are usually difficult to achieve a structure that is mostly hollow inside, resulting in poor lithium storage capacity. Summary of the Invention

[0005] To address the problems of large volume effect, uncontrollable dendrite formation, and low coulombic efficiency in existing alkali metal (Li, Na, K) anodes during cycling, this invention aims to provide an alkali metal-MOF carbon-based composite anode and its alkali metal battery. This anode achieves high alkali metal loading, high energy density, and high performance by loading alkali metal onto a MOF-derived hollow carbon framework. This improves the non-uniformity of alkali metal deposition during high-current cycling, reduces volume effect and interfacial side reactions, and enhances the coulombic efficiency and cycling stability of the alkali metal battery.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: An alkali metal-MOF carbon-based composite anode is prepared by mixing and slurrying MOF-derived hollow carbon framework and adhesive as an active layer, coating it onto a metal current collector, and then filling the active layer with alkali metal. The preparation process of the MOF-derived hollow carbon framework is as follows: (1) Add the transition metal salt to methanol and stir until dissolved to obtain solution A; dissolve 2-methylimidazole in methanol and stir until dissolved to obtain solution B; add solution A to solution B, stir at room temperature and add hexadecyltrimethylammonium bromide, and after aging reaction, obtain MOF material; (2) After adding MOF material to methanol, ultrasonic vibration is performed to disperse it fully. Then, phytic acid dilution is added and the reaction is stirred to obtain hollow carbon framework precursor. (3) The hollow carbon skeleton precursor is carbonized under an inert atmosphere to obtain the MOF-derived hollow carbon skeleton.

[0007] Preferably, in step (1), the cation of the transition metal salt is selected from one of copper, tin, zinc, nickel, aluminum, titanium, silver, iron, magnesium, cobalt, gold, and manganese, and the anion group is selected from CH3COO. − NO3 − PO4 3− Cl − ClO4 − SO4 2− One of them.

[0008] Preferably, in step (1), the molar ratio of the transition metal hydrate: 2-methylimidazole: cetyltrimethylammonium bromide is 1:4~8:0.2~0.5.

[0009] Preferably, in step (1), the aging reaction time is 8 to 24 hours.

[0010] Preferably, in step (2), the mass ratio of MOF material to phytic acid is 1:0.5~1.5, the concentration of phytic acid dilution is 1~3 wt%, and the stirring reaction time is 20~60 min.

[0011] Preferably, in step (3), the inert atmosphere is argon, the carbonization temperature is 500~600 ℃, and the carbonization time is 2~4h.

[0012] This invention employs phytic acid etching of MOF materials. Taking ZIF-67 as an example, the etching process breaks the coordination bond between Co and 2-dimethylimidazole, releasing Co... 2+ Phosphorus-doped shells are obtained by coordination with surface phytic acid. Under inert atmosphere and high temperature carbonization, ZIF-67 is transformed into MOF-derived hollow carbon skeletons with shells rich in nanoparticles such as Co2P2O7, CoP, and CoP2.

[0013] Taking lithium metal as an example, the hollow structure and abundant specific surface area of ​​the MOF-derived hollow carbon skeleton of this invention can effectively reduce local current density, and the partially graphitized carbon matrix has good electron / lithium ion conductivity, which can further homogenize the diffusion of lithium ions / electrons and improve electrode dynamics. The metal phosphide / metal pyrophosphate rich in the shell can effectively improve the lithiophilicity of the MOF-derived hollow carbon skeleton and reduce the lithium nucleation overpotential, induce uniform lithium deposition / stripping, and reduce dendrite growth. Furthermore, the pyrophosphate and phosphide combine with the deposited lithium that gains electrons on the negative electrode side during battery cycling to construct an inorganic-organic composite solid electrolyte interphase (SEI) layer rich in Li3P, LiF, Li3N, Li2O, Li4P2O7, and ROCO2Li on the surface. In addition, Li + The high ionic conductivity SEI film diffuses and deposits into the hollow cavity of the carbon material, while some lithium metal enters the hollow structure through the pores on the material surface. This reduces the volume expansion effect and effectively utilizes the anode space, thereby improving the lithium metal areal capacity density and electrochemical performance of the negative electrode.

[0014] Preferably, the adhesive is one of polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyethylene, polypropylene, polyvinylidene fluoride, SBR rubber, fluorinated rubber, and polyurethane.

[0015] Preferably, the alkali metal filling method is molten alkali metal encapsulation or electrodeposited alkali metal encapsulation.

[0016] An alkali metal battery, such as a Li / Na / KS battery, a Li / Na / KI battery, a Li / Na / K-Se battery, a Li / Na / K-Te battery, a Li / Na / K-O2 battery, etc., includes the above-mentioned alkali metal-MOF carbon-based composite anode.

[0017] The beneficial effects of this invention are: 1. The MOF-derived hollow carbon framework of the present invention ensures structural integrity and stability during uniform alkali metal deposition / dissolution, effectively suppresses interfacial side reactions, and achieves a stable alkali metal anode with high lithium loading and no volume effect, enabling high coulombic efficiency and long cycle life at large current densities.

[0018] 2. The MOF-derived hollow carbon framework of the present invention can effectively reduce local current density and inhibit the growth of alkali metal dendrites. At the same time, it can provide a large amount of filling space and mechanical support for alkali metals. Its surface and interior are rich in alkali metal ion affinity elements, which effectively guide the alkali metals to deposit into its interior and slow down the side reactions at the interface between alkali metals and electrolyte.

[0019] 3. The MOF-derived hollow carbon framework of the present invention, rich in metal phosphide / metal pyrophosphate (such as Co2P2O7, CoP, CoP2) nanoparticles, can effectively reduce the overpotential of alkali metal nucleation and induce selective deposition of alkali metal in its hollow cavity, thus alleviating interfacial side reactions. At the same time, an inorganic-organic composite solid electrolyte interphase (SEI) layer rich in Li3P, LiF, Li3N, Li2O, Li4P2O7, and ROCO2Li is constructed on the surface, so that the material structure can remain intact and stable during repeated alkali metal deposition / dissolution processes.

[0020] In summary, the MOF-derived hollow carbon framework of this invention can accommodate more alkali (Li / Na / K) metals, improving battery energy density and suppressing volume expansion during electrode charging and discharging. The treated hollow biomass carbon material surface incorporates Co2P2O7, CoP, and CoP2 nanoparticles, which can uniformly distribute alkali metal ion flow and concentration on the electrode surface, inducing uniform deposition of alkali metals on the surface and forming a more stable inorganic-organic composite solid-state SEI film, reducing side reactions between the electrode surface and the electrolyte. Furthermore, the surface lithium-philic elements can enhance the affinity for Li. + / Na + / K + The binding energy allows Li / Na / K metals to spontaneously adsorb into the hollow carbon framework, while simultaneously increasing the binding energy of Li. + / Na + / K + The diffusion rate is high, allowing it to be uniformly deposited inside the material and suppressing dendrite formation. Therefore, using the hollow carbon framework of this invention as the Li / Na / K metal anode substrate can effectively suppress Li / Na / K dendrite growth and improve the stability, cycle life, and coulombic efficiency of Li / Na / K metal batteries. Attached Figure Description

[0021] Figure 1SEM images of the samples prepared in Example 1(a), Comparative Example 1(b), and Comparative Example 2(c).

[0022] like Figure 1 As shown, in Example 1, the sample prepared by phytic acid etching still retains its original geometric structure (a); in Comparative Example 1, the sample prepared by small molecule phosphoric acid etching is obviously severely broken (b); in Comparative Example 3, the sample prepared by tannic acid etching can also generate a hollow structure (c).

[0023] Figure 2 TEM images of ZIF-67 carbide material (a) and the MOF-derived hollow carbon skeleton prepared in Example 1 (b).

[0024] like Figure 2 As shown, the ZIF-67 core is etched with phytic acid, and Co is released simultaneously. 2+ Phosphorus-doped shells were obtained by coordination with surface phytic acid. After high-temperature carbonization in an argon atmosphere, ZIF-67 was transformed into a MOF-derived hollow carbon framework with a shell rich in nanoparticles such as Co2P2O7, CoP, and CoP2 (b); while unetched ZIF-67 retained its solid structure after carbonization (a).

[0025] Figure 3 For Example 1 (ZIF-67-PA@C), Comparative Example 1 (ZIF-67-H3PO4@C), and Comparative Example 2 (ZIF-67-TA@C), at 1 mA / cm 2 A schematic diagram showing the results of charge-discharge cycle tests at a given current density. Detailed Implementation

[0026] The following is a detailed description of the preferred embodiments of the present invention, which does not constitute any limitation on the present invention. That is, the present invention is not limited to the following embodiments, and all common variations or alternative compounds in this technical field are included within the scope defined by the claims of this application.

[0027] ZIF-67 is made of the metal Co. 2+ After being stirred and aged in methanol with 2-methylimidazole, the product was obtained by centrifugation, filtration, and drying. The product consists of solid nanoparticles and appears as a purple powder. The specific preparation process is as follows: 0.58 g of cobalt nitrate hexahydrate was added to 20 mL of methanol and stirred until dissolved to obtain a solution; 2-methylimidazole was dissolved in methanol and stirred until dissolved to obtain a solution; the methanol solution of cobalt nitrate hexahydrate was added to the methanol solution of 2-methylimidazole, stirred at room temperature, and hexadecyltrimethylammonium bromide (CTAB) was added and stirred until fully reacted to obtain a mixed solution. After aging, the purple ZIF-67 precipitate was collected by centrifugation, washed with methanol solution, dried, and ground to obtain ZIF-67.

[0028] ZIF-67 was placed in a tube furnace and carbonized by introducing Ar (> 99.99%). The temperature was increased to 550 °C at 2 °C / min and carbonized for 3 hours to obtain ZIF-67 carbonized material.

[0029] Example 1

[0030] Preparation of MOF-derived hollow carbon frameworks: 0.16 g of ZIF-67 was placed in a beaker, and 32 mL of methanol was added. The mixture was ultrasonically vibrated for 15 min to ensure that the ZIF-67 was fully dispersed in the methanol. 2.357 g of phytic acid solution (70% in Water) was dissolved in 100 mL of deionized water, and 8 mL of this solution was added to the suspension containing 0.16 g of ZIF-67. The mixture was magnetically stirred at room temperature for 30 min, then centrifuged. The mixture was washed three times each with anhydrous ethanol and deionized water, and dried in a 60 ℃ forced-air drying oven for 12 h. The dried material was thoroughly ground and placed in a tube furnace. Ar (>99.99%) was introduced for carbonization, and the temperature was increased to 550 ℃ at 2 ℃ / min for 3 h to obtain a MOF-derived hollow carbon framework.

[0031] Preparation of lithium metal-MOF carbon-based composite anodes: Weigh 160 mg of the MOF-derived hollow carbon skeleton from Example 1, 20 mg of acetylene black, and 20 mg of polyvinylidene fluoride (PVDF). Place these three components into a homogenizing tube containing 10-15 zirconium dioxide homogenizing balls. Add a certain amount of N-methylpyrrolidone (NMP) to the homogenizing tube to achieve the desired oily viscosity of the slurry. Seal the tube opening with sealing adhesive to prevent NMP from evaporating during homogenization. Homogenize using a high-speed homogenizer for about 15 minutes to obtain the uniform slurry required for coating. The obtained slurry was coated onto the surface of battery-grade copper foil with a thickness controlled at 60~70 μm. The coated copper foil was dried in a vacuum drying oven at 60 ℃ for 12 h and then cut into circular pieces with a diameter of 12 mm. In an argon atmosphere glove box with a water oxygen content of less than 0.01 ppm, the electrode was used as the working electrode, lithium metal was used as the counter electrode, LS-009 (1 M LiTFSI in DME:DOL=1:1 Vol% with 2% LiNO3) was used as the electrolyte, and glass fiber membrane (Whatman GF / D circular (1823)) was selected as the separator. The membrane was matched with the positive and negative electrode shells and assembled into a button half cell. After that, lithium metal was deposited to prepare the lithium metal-MOF carbon-based composite anode.

[0032] Comparative Example 1 The only difference from Example 1 is that phytic acid is replaced with phosphoric acid.

[0033] Comparative Example 2 The only difference from Example 1 is that phytic acid is replaced with tannic acid.

[0034] The lithium metal carbon-based composite anodes prepared in Example 1 and Comparative Examples 1-2 were used as working electrodes, and lithium metal sheets were used as counter electrodes. Coin cell assembly and charge-discharge cycle tests were conducted using 1 M LiTFSI in DME : DOL = 1 : 1 Vol% with 2% LiNO3 as the electrolyte. The electrolyte was 1 mA / cm². 2 The current density was selected for charge-discharge cycle testing, and the test results are shown in Table 1 below: Table 1. Charge-discharge cycle test results First lap Coulomb efficiency 100th Coulomb efficiency Number of cycles with a Coulomb efficiency below 80% Example 1 91.49% 99.14% 420th Comparative Example 1 80.95% 96.44% 150th Comparative Example 2 82.76% 98.01% 294th The results show that: The electrode prepared in Example 1 exhibits stable charge-discharge cycling, extended cycle life, and improved electrochemical performance. This is because the MOF-derived hollow carbon material shell is rich in composite nanoparticles such as cobalt phosphide and cobalt pyrophosphate. Simultaneously, the thin-walled hollow structure obtained through etching encapsulates lithium metal, which to some extent suppresses interfacial side reactions, reduces polarization voltage, and thus improves the electrode's electrochemical performance.

[0035] The electrode prepared in Comparative Example 1 exhibits unstable charge-discharge cycling, low CE (electric coefficient), short cycle life, and poor electrochemical performance. This is because although cobalt phosphide and cobalt pyrophosphate nanoparticles are generated after carbonization, phosphoric acid cannot form a shell on the ZIF-67 surface, leading to extensive material breakage. The broken material completely loses its ability to accommodate lithium metal. Furthermore, the previously uniformly distributed lithiophilic sites on the material surface are no longer uniform, making it easier for lithium dendrites to form. The broken shell also generates more interfacial side reactions, resulting in a larger polarization voltage and even worse electrochemical performance.

[0036] The electrode prepared in Comparative Example 2, tannic acid-etched ZIF-67, also forms a hollow structure, but its carbon framework only contains CoO and Co3O4 nanoparticles. The SEI film constructed on the surface of this material is only rich in LiF, Li3N, Li2O, ROCO2Li, etc., and its ionic conductivity is far inferior to that of the SEI film in Example 1. + The diffusion rate on the material surface is also lower than that in Example 1, so its effect on inducing lithium metal deposition is not obvious. Therefore, the prepared electrode surface is more prone to lithium dendrite formation than that in Example 1, and the electrochemical performance of the electrode is poor.

Claims

1. An alkali metal-MOF carbon-based composite anode, characterized in that: The active layer is made by mixing and slurrying MOF-derived hollow carbon framework and adhesive, coating it onto a metal current collector, and then filling the active layer with alkali metal to obtain an alkali metal-MOF carbon-based composite anode. The preparation process of the MOF-derived hollow carbon framework is as follows: (1) Add the transition metal salt to methanol and stir until dissolved to obtain solution A; dissolve 2-methylimidazole in methanol and stir until dissolved to obtain solution B; add solution A to solution B, stir at room temperature and add hexadecyltrimethylammonium bromide, and after aging reaction, obtain MOF material; (2) After adding MOF material to methanol, ultrasonic vibration is performed to disperse it fully. Then, phytic acid dilution is added and the reaction is stirred to obtain hollow carbon framework precursor. (3) The hollow carbon skeleton precursor is carbonized under an inert atmosphere to obtain the MOF-derived hollow carbon skeleton.

2. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: In step (1), the cation of the transition metal salt is selected from one of copper, tin, zinc, nickel, aluminum, titanium, silver, iron, magnesium, cobalt, gold, and manganese, and the anionic group is selected from CH3COO. − NO3 − PO4 3− Cl − ClO4 − SO4 2− One of them.

3. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: In step (1), the molar ratio of the transition metal salt hydrate: 2-methylimidazole: cetyltrimethylammonium bromide is 1:4~8:0.2~0.

5.

4. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: In step (1), the aging reaction takes 8 to 24 hours.

5. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: In step (2), the mass ratio of MOF material to phytic acid is 1:0.5~1.5, the concentration of phytic acid dilution is 1~3 wt%, and the stirring reaction time is 20~60 min.

6. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: In step (3), the inert atmosphere is argon, the carbonization temperature is 500~600 ℃, and the carbonization time is 2~4 h.

7. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: The adhesive is one of the following: polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyethylene, polypropylene, polyvinylidene fluoride, SBR rubber, fluorinated rubber, and polyurethane.

8. The alkali metal-MOF carbon-based composite anode according to claim 1, characterized in that: The method of filling with alkali metal is either molten alkali metal encapsulation or electrodeposited alkali metal encapsulation.

9. An alkali metal battery, characterized in that: The alkali metal-MOF carbon-based composite anode includes any one of claims 1-8.

10. The alkali metal battery according to claim 9, characterized in that: The alkali metal battery is a Li / Na / KS battery, a Li / Na / KI battery, a Li / Na / K-Se battery, a Li / Na / K-Te battery, or a Li / Na / K-O2 battery.

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