阅读说明：本技术 具有硫纳米结构的蛋黄和碳化的金属有机骨架壳的多孔材料及其用途 (Porous material of yolk with sulfur nanostructure and carbonized metal organic framework shell and use thereof ) 是由 刘云阳 伊哈卜·N·乌达 于 2018-06-14 设计创作，主要内容包括：描述了具有蛋黄-壳结构的多孔碳材料、其制备方法和用途。多孔碳材料可具有位于多孔碳化金属有机骨架(MOF)壳的中空空间内的硫基蛋黄。(Porous carbon materials having a yolk-shell structure, methods of making, and uses thereof are described. The porous carbon material may have a sulfur-based yolk located within the hollow space of the porous metal carbide organic framework (MOF) shell.)

1. A porous material having a yolk-shell type structure, the porous material comprising a sulfur-based material disposed within hollow spaces of a porous carbonized Metal Organic Framework (MOF) shell, wherein the porous carbonized MOF shell is doped with nitrogen.

2. The porous material of claim 1, wherein the porous shell comprises 2 to 40 weight percent elemental nitrogen (N), 25 to 35 weight percent N, or 27 to 32 weight percent N, with the remainder being elemental carbon.

3. The porous material of claim 1, wherein the MOF is a Zeolitic Imidazolate Framework (ZIF).

4. The porous material of claim 3, wherein ZIF is:

ZIF-1 to ZIF-100, preferably ZIF-8; or

Hybrid ZIFs, preferably ZIF7-8, ZIF8-90, ZIF 7-90.

5. The porous material of claim 1 wherein the carbon shell is substantially defect-free.

6. The porous material of claim 1, wherein the hollow spaces allow volume expansion of sulfur-based nanostructures without deforming the porous carbonized shell, preferably volume expansion of at least 50%.

7. The porous material of claim 1, wherein the sulfur-based material is elemental sulfur or lithium sulfide.

8. A method of preparing a porous material having a yolk-shell structure, the method comprising:

(a) combining an organic framework precursor with a suspension comprising zinc oxide (ZnO) under conditions suitable to produce a Metal Organic Framework (MOF) material comprising a ZnO core and an organic framework shell, wherein the organic framework shell comprises the ZnO core;

(b) heat treating the MOF material under conditions sufficient to carbonize the organic framework shell to produce a core-shell material comprising a ZnO core and a porous carbonized shell;

(c) subjecting the ZnO core-porous carbonized shell material of step (b) to conditions sufficient to remove the ZnO and form a hollow porous carbonized shell material; and

(d) sulfur-based materials are incorporated into the hollow spaces of the carbonized shell to form a yolk-shell structure having sulfur-based nanostructures located within the hollow spaces of the porous carbonized shell.

9. The method of claim 8, wherein the ZnO suspension comprises zinc oxide (ZnO), an alcohol, and water.

10. The method of claim 8, wherein the conditions of step (a) comprise stirring the suspension for a time sufficient for the organic framework precursor to self-assemble around the ZnO.

11. The method of claim 8, wherein heat treating comprises heating to a temperature of 550 ℃ to 1100 ℃ under an inert atmosphere to carbonize the shell of the MOF and form a porous carbonized shell.

12. The process according to claim 8, wherein the conditions of step (c) comprise contacting the ZnO core-porous carbonized shell material with a mineral acid, preferably HCl.

13. The method of claim 8, wherein the incorporating of step (d) comprises contacting the hollow carbonized shell material with a sulfur-based material under conditions suitable for diffusing the sulfur-based material into the hollow spaces of the carbonized shell material.

14. The method of claim 8, wherein the organic framework precursor is a bidentate carboxylate, a tridentate carboxylate, an amino-substituted aromatic dicarboxylic acid, an amino-substituted aromatic tricarboxylic acid, an azido-substituted aromatic dicarboxylic acid, an azido-substituted aromatic tricarboxylic acid, a triazole, a substituted triazole, an imidazole, a substituted imidazole, or a mixture thereof, preferably 2-methylimidazole.

15. The method of claim 8, wherein the porous carbonized shell is defect free.

16. The method of claim 8, wherein the sulfur-based material is elemental sulfur or lithium sulfide.

17. An energy storage device comprising the porous material having a yolk-shell type structure of claim 1.

18. The energy storage device of claim 17, wherein the energy storage device is a rechargeable battery, preferably a lithium sulfur battery.

19. The energy storage device of claim 17, wherein the porous material having a yolk-shell type structure is included in an electrode of the energy storage device.

20. The energy storage device of claim 19, wherein the electrode is a cathode, an anode, or both.

Background

A. Field of the invention

The present invention relates generally to porous materials having a yolk-shell type structure that can be used in energy storage devices. Specifically, the porous material includes a sulfur-based nanostructured egg yolk located within the hollow spaces of a porous metal carbide organic framework (MOF) shell.

B. Description of the related Art

Global energy demand has steadily increased. This may have a negative impact on the environment unless safer, cheaper and/or more environmentally friendly energy storage options with high energy storage densities are developed. Lithium-sulfur (Li-S) batteries are the most promising energy storage devices. In recent years, 1672mAh g is used^-1Which is more than 5 times the high theoretical capacity of the currently used transition metal oxide cathode materials, these batteries are of interest. Additionally, Li-S batteries can be manufactured at relatively low cost, due in part to the abundant natural sulfur resources. In addition, these batteries are relatively non-toxic and environmentally friendly compared to other energy storage devices. However, the practical application of Li-S batteries is still limited by at least the following disadvantages: 1) poor conductivity of sulfur (5X 10)^-30S cm^-1) This limits the efficiency of utilization and rate capability of the active material; 2) the high solubility of polysulfide intermediates in the electrolyte leads to shuttling effects during charging and discharging; 3) volume expansion is large (about 80%) during charging and discharging, resulting in rapid capacity fade and low coulombic efficiency.

During charge and discharge cycles of Li-S batteries, electrochemical cleavage and recombination of sulfur-sulfur bonds may occur. In particular, sulfur is reduced to higher-order lithium polysulfides (Li)₂S_nWhere n is 4. ltoreq. n.ltoreq.8), thenFurther reduction to low-order lithium polysulfide (Li)₂S_nWherein n is more than or equal to 1 and less than or equal to 3). Higher order polysulfides can be dissolved into the organic liquid electrolyte, enabling them to pass through the polymer separator between the anode and cathode and then react with the lithium metal anode, resulting in loss of sulfur active material. Even if some of the dissolved polysulfides diffuse back to the cathode during recharging, the sulfur particles formed on the cathode surface are not electrochemically active due to poor electrical conductivity. Such fading paths result in poor capacity retention, particularly during long cycles (e.g., over 100 cycles).

Various attempts to improve Li-S batteries while inhibiting polysulfide dissolution and shuttling have been described. For example, chinese patent application publication No. 105384161 to Zhang et al describes a sulfur-containing hierarchical porous carbon material prepared by mixing elemental sulfur with a hierarchical porous carbon material made of zinc carbide ZIF. In another example, U.S. patent No. 9437871 to Zhou et al describes a polymer coated carbon shell having a sulfur core. In yet another example, Zhang et al, chinese patent application publication No. 10533379 and jayarrakasah et al (angelw. chem. int.ed.,2011,50,5904) describe core-shell structures having a sulfur core and a calcined carbon shell made of phenolic resin or petroleum pitch, respectively.

Despite all available research on Li-S based energy storage devices, many of these devices still suffer from capacity fade during charge and discharge cycles. These devices may also suffer from complex and environmentally unfriendly manufacturing schemes, low active material loading, and/or reduced electrical conductivity, any of which may result in unsatisfactory overall electrochemical performance.

Disclosure of Invention

Solutions to some of the problems associated with the swelling and de-swelling of carbon-based materials and the shuttling effect of polysulfides have been found. The solution lies in the ability to design a yolk-shell material that is capable of absorbing metal ions (e.g., lithium ions) while reducing or inhibiting the dissolution of polysulfides. In particular, the sulfur-based material is located within the hollow space of a metal carbide organic framework (MOF) shell. The nanostructured element sulfur yolk may absorb metal ions (e.g., lithium ions) and expand (e.g., at least 50% volume expansion) in the void spaces of the porous carbonized shell without deforming/expanding the shell. In a preferred aspect, the porous carbonized MOF shell can include nitrogen. Nitrogen doping can increase the absorption of sulfur compounds, thereby reducing polysulfide dissolution. The methods of the invention also provide a compact method of incorporating nitrogen into porous carbonized MOF shells. For example, MOF precursors comprising nitrogen atoms can be used to grow nitrogen-doped (N-doped) organic framework shells in situ on a metal oxide (e.g., ZnO) surface to form nitrogen-doped MOF core-shell structures. After carbonization and removal of the metal oxide, hollow carbon spheres may be formed. A sulfur-based material (e.g., elemental sulfur or lithium sulfide) may then be incorporated (e.g., impregnated) into the hollow carbon spheres to form a sulfur/nitrogen doped carbonized yolk/shell structure. Such a method can produce a substantially or completely defect-free porous nitrogen-doped carbonized shell encapsulating a sulfur-based egg yolk. The resulting materials are useful in energy storage devices.

In one aspect of the invention, a porous material having a yolk-shell type structure is described. The porous material may include a sulfur-based material located within the hollow spaces of a porous metal carbide organic framework (MOF) shell. The carbonized shell may be defect free (e.g., the shell is a continuous surface). In some embodiments, the shell is nitrogen doped. The N-doped shell may comprise 2 to 40, 25 to 35, or 27 to 32 weight percent elemental nitrogen, with the remainder being elemental carbon. In some embodiments, the MOF may be a Zeolitic Imidazolate Framework (ZIF) (e.g., ZIF-1 to ZIF-100, hybrid ZIF, ZIF7-8, ZIF8-90, ZIF7-90, functionalized ZIF, ZIF-8-90, ZIF7-90, preferably ZIF is ZIF-8). The sulfur-based material may be elemental sulfur or lithium sulfide.

A method of making a porous material having a yolk-shell structure is described. The method may comprise at least four steps, step (a) to step (d). In step (a), the Organic Framework (OF) precursor may comprise at least one metal oxide (e.g. zinc oxide (ZnO), magnesium oxide) under conditions suitable for the manufacture OF a metal-organic framework (MOF) material having a core-shell structure(MgO), iron oxide (FeO and/or Fe)₂O₃) Strontium oxide (SrO), nickel oxide (NiO), cobalt oxide (CoO and/or Co)₂O₃) Calcium oxide (CaO), cadmium oxide (CdO), copper oxide (CuO), or mixtures thereof), the core-shell structure having a metal oxide core and an organic framework shell. The organic framework shell may comprise carbon atoms and nitrogen atoms. The metal oxide suspension can comprise a metal oxide (e.g., zinc oxide (ZnO)), an alcohol, and water. The organic framework precursor may be a bidentate carboxylate, a tridentate carboxylate, an amino-substituted aromatic dicarboxylic acid, an amino-substituted aromatic tricarboxylic acid, an azido-substituted aromatic dicarboxylic acid, an azido-substituted aromatic tricarboxylic acid, a triazole, a substituted triazole, an imidazole, a substituted imidazole, or mixtures thereof, preferably 2-methylimidazole. The conditions in step (a) may comprise stirring the suspension for a sufficient time to allow the organic framework to self-assemble around the metal oxide (e.g. stirring for 15 to 60 minutes at 0 to 100 ℃) to form the nitrogen doped MOF. In step (b) of the method, the nitrogen-doped MOF material can be heat treated under conditions sufficient to carbonize the organic framework shell to produce a core-shell material comprising a metal oxide (e.g., ZnO) core and a porous carbonized shell. The heat treatment can include heating the nitrogen-doped MOF core-shell material to 550 ℃ to 1100 ℃ under an inert atmosphere to carbonize the organic framework and form a porous carbonized shell surrounding a metal oxide core (e.g., a ZnO core). Step (c) of the method may comprise subjecting the metal oxide core-porous carbonized shell material of step (b) to conditions sufficient to remove the metal oxide core and form a hollow porous carbonized shell material. The conditions of step (c) may comprise contacting the metal oxide core-porous carbonized shell material with a mineral acid, preferably HCl. In step (d) of the method, an elemental sulfur-based material may be incorporated into the hollow spaces of the carbonized shell to form a yolk-shell structure having sulfur-based nanostructures located in the porous carbonized shell hollow spaces. The incorporation of elemental sulfur-based material of step (d) may comprise contacting the hollow carbonized shell material with a sulfur-based material under conditions suitable to diffuse the sulfur-based material into the hollow spaces of the carbonized shell material. In some embodiments, the sulfur-based material is elemental sulfur or sulfidedLithium, or both.

In some aspects of the present disclosure, an energy storage device is described. The energy storage device may comprise a porous material having a yolk-shell type structure of the invention. In some embodiments, the porous materials of the present invention are incorporated into electrodes of energy storage devices. In particular, the porous material may be incorporated into the cathode of such a device or into the anode of such a device.

In the context of the present invention, 20 embodiments are described. Embodiment 1 is a porous material having a yolk-shell type structure comprising a sulfur-based material disposed within hollow spaces of a porous carbonized Metal Organic Framework (MOF) shell, wherein the porous carbonized MOF shell is doped with nitrogen. Embodiment 2 is the porous material of embodiment 1, wherein the porous shell comprises 2 to 40 weight percent elemental nitrogen (N), 25 to 35 weight percent N, or 27 to 32 weight percent N, with the remainder being elemental carbon. Embodiment 3 is the porous material of any one of embodiments 1 to 2, wherein the MOF is a Zeolitic Imidazolate Framework (ZIF). Embodiment 4 is the porous material of any one of embodiments 1 to 3, wherein the ZIF is ZIF-1 to ZIF-100, preferably ZIF-8; or hybrid ZIFs, preferably ZIF7-8, ZIF8-90, ZIF 7-90. Embodiment 5 is the porous material of any one of embodiments 1 to 4, wherein the carbon shell is substantially defect-free. Embodiment 6 is the porous material of any one of embodiments 1 to 5, wherein the hollow space allows volume expansion of the sulfur-based nanostructures without deforming the porous carbonized shell, preferably the volume expansion is at least 50%. Embodiment 7 is the porous material of any one of embodiments 1 to 6, wherein the sulfur-based material is elemental sulfur or lithium sulfide.

Brief description of the drawings

Advantages of the present invention will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the accompanying drawings.

Fig. 1A to 1B are schematic views of a porous carbon material having a yolk-shell structure.

Fig. 2 is a schematic diagram of an embodiment of a method of preparing a porous carbon material having a yolk-shell structure.

Fig. 3A-3H depict Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images of (fig. 3A and 3B) ZnO, (fig. 3C and 3D) Zn @ ZIF-8 core-shell, (fig. 3E and 3F) N-doped Carbon Hollow Shell (CHS) material, and (fig. 3G and 3H) S @ C material derived from the CHS material of fig. 3E and 3F of the present invention.

Fig. 4A to 4D depict (fig. 4A) a simulated XRD pattern (bottom pattern) of ZnO and XRD patterns of synthesized ZnO; (FIG. 4B) simulated XRD pattern of ZnO (middle pattern), XRD simulation of ZIF-8 (bottom pattern) and XRD pattern of ZnO @ ZIF-8 (top pattern); (FIG. 4C) XRD pattern of ZnO @ ZIF-8 (bottom pattern), simulated XRD pattern of ZnO (second pattern from bottom), XRD pattern of ZnO @ C (third pattern from bottom), and XRD pattern of HCS (top pattern); (FIG. 4D) XRD pattern of sulfur (bottom pattern) and XRD pattern of S @ C (top pattern).

Figure 5 shows a thermogravimetric analysis (TGA) of the S @ C yolk-shell composite of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

Embodiment 8 is a method of making a porous material having a yolk-shell structure, the method comprising: (a) combining an organic framework precursor with a suspension comprising zinc oxide (ZnO) under conditions suitable to produce a Metal Organic Framework (MOF) material comprising a ZnO core and an organic framework shell, wherein the organic framework shell comprises the ZnO core; (b) heat treating the MOF material under conditions sufficient to carbonize the organic framework shell to produce a core-shell material comprising a ZnO core and a porous carbonized shell; (c) subjecting the ZnO core-porous carbonized shell material of step (b) to conditions sufficient to remove the ZnO and form a hollow porous carbonized shell material; and (d) incorporating a sulfur-based material into the hollow space of the carbonized shell to form a yolk-shell structure having sulfur-based nanostructures located within the hollow space of the porous carbonized shell. Embodiment 9 is the method of embodiment 8, wherein the ZnO suspension comprises zinc oxide (ZnO), alcohol, and water. Embodiment 10 is the method of any one of embodiments 8 to 9, wherein the conditions of step (a) include stirring the suspension for a time sufficient for the organic framework precursor to self-assemble around the ZnO. Embodiment 11 is the method of any one of embodiments 8 to 10, wherein the heat treating comprises heating to a temperature of 550 ℃ to 1100 ℃ under an inert atmosphere to carbonize the shell of the MOF and form a porous carbonized shell. Embodiment 12 is the method of any one of embodiments 8 to 11, wherein the conditions of step (c) comprise contacting the ZnO core-porous carbonized shell material with a mineral acid, preferably HCl. Embodiment 13 is the method of any one of embodiments 8 to 12, wherein the incorporating of step (d) includes contacting the hollow carbonized shell material with a sulfur-based material under conditions suitable to diffuse the sulfur-based material into the hollow spaces of the carbonized shell material. Embodiment 14 is the method of any one of embodiments 8 to 13, wherein the organic framework precursor is a bidentate carboxylate, a tridentate carboxylate, an amino-substituted aromatic dicarboxylic acid, an amino-substituted aromatic tricarboxylic acid, an azido-substituted aromatic dicarboxylic acid, an azido-substituted aromatic tricarboxylic acid, a triazole, a substituted triazole, an imidazole, a substituted imidazole, or a mixture thereof, preferably 2-methylimidazole. Embodiment 15 is the method of any one of embodiments 8 to 14, wherein the porous carbonized shell is defect free. Embodiment 16 is the method of any one of embodiments 8 to 15, wherein the sulfur-based material is elemental sulfur or lithium sulfide.