Carbon quantum dot material, and preparation method and application thereof

Abstract

The application discloses a kind of carbon quantum dot materials and its preparation method and application, specifically related to the field of battery material.It includes: p-xylylene formaldehyde and p-trifluoromethyl phenyl cyanide acetonitrile are placed in sodium methoxide solution to carry out hydrothermal reaction, obtain carbon quantum dot material;PAN powder is mixed with DMF to obtain PAN spinning solution;Carbon quantum dot material is dispersed in PAN spinning solution, to obtain mixed spinning liquid;Mixed spinning liquid is spun on the surface of zinc foil by electrostatic spinning, to obtain modified zinc foil.Carbon quantum dot material rich in multiple types of zincophilic functional groups synthesized by hydrothermal method strategy can improve the electric field distribution of zinc metal surface, and then uniform zinc ion deposition and nucleation process, avoid zinc dendrite formation, use modified zinc foil as the anode material of aqueous zinc ion battery, and carbon quantum dot material with abundant negative electric functional groups can repel sulfate ions in electrolyte, to inhibit the formation of byproduct.

Description

Technical Field

[0001] This application relates to the field of battery materials, and particularly to a carbon quantum dot material, a preparation method thereof, and an application thereof. Background Art

[0002] Regarding the reserves in nature, the studied aqueous ion batteries include alkali metal cations (Li + , Na + and K + ) and polyvalent ion (Ca 2+ , Mg 2+ , Al 3+ and Zn 2+ ) batteries. Aqueous sodium-ion batteries and potassium-ion batteries have large raw material reserves and low production costs, and have chemical properties similar to lithium. However, they face problems such as low energy density and high toxicity. Although polyvalent ions can be used for redox reactions involving multiple electrons to obtain high specific capacity and high energy density, there are still some problems. For example, the deposition and dissolution reversibility of the negative electrode of aqueous calcium-ion batteries is poor, and the electrolyte will cause corrosion of the negative electrode and the current collector, resulting in unstable battery performance. In aqueous magnesium-ion batteries, Mg 2+ diffuses slowly in the host lattice, there are few available positive electrode materials, and the magnesium negative electrode is prone to passivation, further hindering the diffusion of Mg 2+ . Although aqueous aluminum-ion batteries have a high volume capacity (8040 mAh cm -3 ), the aluminum negative electrode is prone to form an A12O3 passivation film on the surface in an aqueous electrolyte (4 < pH < 8) and is prone to cause uneven corrosion of the aluminum electrode surface, resulting in attenuation of battery efficiency and electrode potential, making the aqueous aluminum-ion battery still in the experimental stage and limited to the field of primary battery energy storage. In comparison, aqueous zinc-ion batteries use a mild neutral electrolyte, have a high theoretical capacity, a relatively low redox potential, low production costs, and high safety, and stand out among multi-ion aqueous batteries and are expected to be applied in the fields of power grid energy storage and electric vehicles in the future.

[0003] Currently, commercial zinc foil is commonly used as the negative electrode material for aqueous zinc-ion batteries. Although zinc anodes have high capacity, they are susceptible to zinc dendrite formation and hydrogen evolution reactions during charge and discharge, leading to battery short circuits and internal expansion, resulting in irreversible zinc anode loss and shortening battery life. The formation of zinc dendrites is primarily due to the electric field and the uneven distribution of Zn2+ on the anode surface, while the hydrogen evolution reaction is caused by the slow corrosion of the zinc metal anode in the aqueous electrolyte and the decomposition of the electrolyte during battery cyclic charge and discharge. Repeated deposition / stripping of metallic zinc leads to evolution of the electrode-electrolyte interface (i.e., changes in interface shape). The deposition / stripping process is typically non-uniform, resulting in irregular surface morphology and zinc dendrite growth, a phenomenon known as the "tip effect." In practical zinc-ion battery devices, dendritic deposition of the zinc anode and related side reactions (hydrogen evolution reaction, corrosion, and passivation) caused by free water hinder further development and significantly limit the cycle life of aqueous zinc-ion batteries. Based on the challenges encountered with zinc anodes, those skilled in the art have proposed several design strategies, including host material design, alloying design, and interface modification. The design of a host material typically utilizes a porous 3D anode, which, due to its large surface area, effectively inhibits passivation. Furthermore, the 3D anode reduces local current density and promotes uniform ion distribution, thereby achieving uniform Zn deposition. Furthermore, the voids within the framework provide ample space for Zn deposition, partially preventing short-circuiting issues caused by dendrite growth. However, all host material design approaches present challenges, such as electrode deformation and corrosion at high utilization rates, as well as increased volume and reduced energy density due to alloying. Alloying Zn with other elements can modify the physical and chemical properties of the interface, enhancing corrosion resistance, mitigating passivation effects, and reducing the formation of dead Zn. This approach holds promise for improving the practical utilization and overall performance of Zn in secondary batteries. The synergistic effects of different elements can significantly enhance the corrosion resistance and hydrogen evolution overpotential of alloyed Zn anodes. However, alloyed Zn anodes somewhat compromise the advantage of high theoretical specific capacity and tend to rapidly fail due to interface reconstruction during battery charging. Furthermore, the use of bulk Zn alloy anodes significantly increases cost and reduces energy density. Interface modification strategies mainly include two methods: electrolyte additives and the construction of artificial protective layers. The negative electrode is in direct contact with the electrolyte, and the interface between the two is where zinc deposition and dissolution occur. In addition to the inherent self-modification of the zinc negative electrode, the electrolyte also plays an important role in affecting the performance of the negative electrode. The properties and composition of the electrolyte have a significant impact on the electrochemical behavior, stability and overall performance of the negative electrode. Therefore, changing the composition of the electrolyte or the negative electrode with certain additives can enhance the stability and reversibility of the system. Although preliminary results have been achieved in using additives to solve various problems related to the zinc negative electrode in the system, the development of multifunctional additives is still relatively difficult. Most additives are single-functional, such as only focusing on dendrite growth problems or interface side reactions.In addition, the existing artificial protective layers on the surface of zinc negative electrodes mostly rely on expensive equipment, such as magnetron sputtering and atomic layer deposition (ALD), which is not conducive to the large-scale application of modified zinc negative electrodes. Summary of the Invention

[0004] The main purpose of this application is to provide a carbon quantum dot material and its preparation method and application, which can simultaneously avoid the formation of zinc dendrites and the occurrence of interfacial side reactions.

[0005] To achieve the above objectives, the present application provides a method for preparing a carbon quantum dot material, comprising: placing terephthalaldehyde and trifluoromethylbenzonitrile acetonitrile in a sodium methoxide solution for hydrothermal reaction to obtain a carbon quantum dot material.

[0006] Optionally, the mass ratio of terephthalaldehyde to trifluoromethylbenzonitrile is 1:1-2.

[0007] Optionally, the temperature of the hydrothermal reaction is 120-180° C., and the time is 1-5 h.

[0008] Optionally, the sodium methoxide concentration is 0.5-1.5 mol L -1 .

[0009] To achieve the above objectives, the present application also provides a carbon quantum dot material, which is obtained by the above-mentioned method for preparing the carbon quantum dot material, and the carbon quantum dot material has zinc-philic nucleation sites.

[0010] To achieve the above-mentioned purpose, the present application also provides a method for preparing a modified zinc foil, comprising: mixing PAN powder with DMF to obtain a PAN spinning solution; dispersing a carbon quantum dot material in the PAN spinning solution to obtain a mixed spinning liquid; and spinning the mixed spinning liquid onto the surface of the zinc foil by electrospinning to obtain a modified zinc foil.

[0011] Optionally, the mass ratio of PAN powder to DMF is 0.5-1:9, and the mass ratio of carbon quantum dot material to PAN powder is 0.5-1:10.

[0012] Optionally, the electrospinning process specifically includes: pouring the mixed spinning liquid into a syringe, wrapping the zinc foil on the surface of the receiving device, and performing directional spinning at 45-60 degrees to the receiving device; the electrospinning speed is 0.5-2 mL h -1 , the drying time is 4-8 h.

[0013] To achieve the above objectives, the present application also provides a modified zinc foil obtained by the above-mentioned preparation method of the modified zinc foil.

[0014] To achieve the above objectives, the present application also provides an application of a modified zinc foil in a negative electrode material of a zinc ion battery.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The preparation method of the carbon quantum dot material of the present invention is to synthesize a carbon quantum dot material rich in various types of zinc-philic functional groups through a hydrothermal method, which can improve the electric field distribution on the surface of zinc metal, thereby uniformly depositing zinc ions and nucleating the process, and avoiding the formation of zinc dendrites. The preparation method of the modified zinc foil of the present invention provides a strong guarantee for the adhesion of the protective layer to the zinc metal due to the high adhesion of the spinning material and the interaction between the large amount of fluorine elements in the carbon quantum dots and the zinc metal, thereby forming a protective layer with excellent mechanical properties, which can effectively inhibit volume expansion during high current or high capacity cycling; it has good cyclability during the charge and discharge process, and due to the strong adhesion, the protective layer will not fall off due to failure phenomena such as failure; the internally doped carbon quantum dot material contains a large number of polar functional groups, thereby improving the ionic conductivity of the material to a certain extent; the modified zinc foil of the present invention, as the negative electrode material of the aqueous zinc ion battery, has a carbon quantum dot material rich in negatively charged functional groups that can repel sulfate ions in the electrolyte, thereby inhibiting the formation of by-products; the simple operation of the electrospinning process is expected to accelerate the large-scale application of the modified negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a TEM image of a carbon quantum dot material for this application;

[0018] Figure 2 for Figure 1 FT-IR image of carbon quantum dot material;

[0019] Figure 3 A schematic diagram of the synthesis of a modified zinc foil for this application;

[0020] Figure 4 This is the SEM image of Zn@PCDs prepared in Example 1;

[0021] Figure 5 This is the structural diagram of Zn@PCDs prepared in Example 1;

[0022] Figure 6 Schematic diagram of the mechanism of Zn@PCDs prepared in Example 1 being used as the negative electrode of zinc ion battery;

[0023] Figure 7 This is a rate performance diagram of the PCDs composite material prepared in Example 1 under different current density conditions;

[0024] Figure 8 This is a long cycle performance diagram of the PCDs composite material prepared in Example 1 under different current density conditions.

[0025] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0027] A first embodiment of the present invention provides a method for preparing a carbon quantum dot material, which specifically includes the following steps:

[0028] Step S1: Place terephthalaldehyde and trifluoromethylbenzonitrile in a sodium methoxide solution for hydrothermal reaction to obtain a carbon quantum dot material. The specific steps may be:

[0029] According to the mass ratio of 1:1-2, first dissolve trifluoromethylbenzonitrile in 50 mL of 0.5-1.5 mol L -1 The mixture was added to a sodium methoxide solution and stirred for 10-20 minutes until the substances were uniformly dispersed to obtain a mixed solution; terephthalaldehyde was then added to the mixed solution, and ultrasonic treatment was performed for 10-20 minutes to obtain a mixed reaction liquid. The mixed reaction liquid was then transferred to an autoclave, and hydrothermally reacted at 120-180°C for 1-5 hours. After naturally cooling to room temperature, the reaction product was purified to obtain FN-CDs material, i.e., carbon quantum dot material.

[0030] The purification process can be as follows: dilute the mixture with 100 mL of deionized water, then centrifuge with water and acetone at 10,000 rpm for 10 minutes to remove the supernatant, and finally dry in a vacuum oven at 80° C. for 10 hours.

[0031] In this embodiment, the carbon quantum dot material rich in various types of zinc-philic functional groups synthesized by the hydrothermal strategy can improve the electric field distribution on the zinc metal surface, thereby uniformizing the zinc ion deposition and nucleation process.

[0032] Carbon quantum dot materials were synthesized by dehydration condensation of terephthalaldehyde and trifluoromethylbenzonitrile acetonitrile.

[0033] The second embodiment of the present invention provides a carbon quantum dot material. It can provide a large number of zinc-philic sites and improve the surface electric field, promote the transport process of zinc ions, and make it have excellent cycle stability.

[0034] A third embodiment of the present invention provides a method for preparing a modified zinc foil, which specifically includes the following steps:

[0035] Step S2, mixing polyacrylonitrile (PAN) powder and DMF in a mass ratio of 0.5-1:9 to obtain a PAN spinning solution;

[0036] Step S3, dispersing the carbon quantum dot material in the PAN spinning solution at a mass ratio of the carbon quantum dot material to the PAN powder of 0.5-1:10, and magnetically stirring for 6 hours to obtain a PCDs mixed solution, i.e., a mixed spinning liquid; wherein the carbon quantum dot material is the carbon quantum dot material described above;

[0037] Step S4: Spin the mixed spinning liquid onto the surface of the zinc foil by electrospinning. Specifically, the mixed spinning liquid is poured into a syringe, and the zinc foil is wrapped on the surface of the receiving device (drum). The spinning is performed at an angle of 45-60 degrees to the receiving device. The electrospinning speed is 0.5-2 mL h -1 After the electrospinning is completed, the drying time is 4-8 h to obtain Zn@PCDs, that is, modified zinc foil.

[0038] In this embodiment, the PCDs fiber layer is obtained by combining the carbon quantum dot material and PAN powder through electrospinning technology. Due to the potential difference, the spinning solution is randomly and evenly sprayed on the surface of the zinc foil by the needle to form a large number of porous structures. The high molecular weight of the PAN material ensures the high elasticity and high toughness of the fiber, thereby forming a protective layer with excellent mechanical properties, which can effectively inhibit volume expansion during high current or high capacity cycles. The internally doped carbon quantum dot material contains a large number of polar functional groups, thereby improving the ionic conductivity of the material to a certain extent. The large amount of F elements inside can enhance the bonding force between the protective layer and the zinc metal and reduce the surface energy of the zinc (002) crystal plane, so that the zinc ions preferentially deposit on the (002) crystal plane.

[0039] The fourth embodiment of the present invention provides a modified zinc foil obtained by the above-mentioned method for preparing the modified zinc foil.

[0040] A fifth embodiment of the present invention provides an application of a modified zinc foil in a negative electrode material of a zinc ion battery.

[0041] The modified zinc foil is used as the negative electrode material for aqueous zinc ion batteries. The carbon quantum dot material with abundant negatively charged functional groups can repel sulfate ions in the electrolyte, thereby inhibiting the formation of by-products. The F element reduces the binding energy of the zinc (002) crystal plane to a certain extent, and the zinc ion (002) crystal plane is preferentially deposited. In addition, the zinc-philic hydrophobic protective layer can reduce [Zn(H2O)6] 2+ The desolvation energy barrier facilitates rapid desolvation and nucleation processes while suppressing side reactions. Therefore, the protective layer deposited on the surface of the zinc negative electrode by the preparation method of the present invention can ensure uniform and stable deposition of the zinc metal negative electrode at different current densities.

[0042] Example 1

[0043] Step S10, dissolve 13 g of trifluoromethylbenzonitrile in 50 mL of 1 mol L -1 The mixture was then added to a sodium methoxide solution and stirred for 10 minutes until uniformly dispersed. Subsequently, 10 g of terephthalaldehyde was added to the mixture and sonicated for 10 minutes. The solvent was then transferred to an autoclave and hydrothermally reacted at 160°C for 2 hours. After cooling to room temperature, the mixture was diluted with 100 mL of deionized water and centrifuged at 10,000 rpm for 10 minutes with water and acetone, and the supernatant was removed. Finally, the mixture was dried in a vacuum oven at 80°C for 10 hours to obtain the FN-CDs material, i.e., the carbon quantum dot material.

[0044] The FN-CDs material obtained in this example was tested, and the test results are shown in Figure 1-2 , Figure 1 The spots in the image are carbon quantum dots. Figure 1 It can be seen that the size distribution of carbon quantum dots is uniform, and the diameter is about 3 nm. Figure 2 Fourier transform infrared (FT-IR) analysis of the surface functional groups of CDs ( Figure 2 ). Apparently, 1687 and 2220 cm –1 The peaks near 1300 cm are associated with the stretching of -CHO and -CN groups. –1 The peak is reached near 300 nm, which can be attributed to the CF stretching, further indicating the successful preparation of surface FN-CDs, whose rich internal functional groups are expected to provide more zinc-philic deposition sites and improve zinc anode deposition.

[0045] Step S20, mixing PAN powder and DMF at a mass ratio of 1:9 to obtain a PAN spinning solution;

[0046] Step S30, transferring the FN-CDs into the PAN spinning solution and magnetically stirring for 6 h to obtain a PCDs mixed solution;

[0047] Step S40: Pour the PCDs mixed solution into the syringe, wrap the zinc foil on the surface of the drum, and perform directional spinning at a 45° angle to the drum at a spinning rate of 1 mL h -1 , Zn@PCDs, i.e. modified zinc foil, is obtained. The synthesis diagram is shown in Figure 3 shown.

[0048] The Zn@PCDs modified negative electrode obtained in this embodiment was tested, and the test results are shown in Figure 4 ,from Figure 4 From the SEM images at different magnifications, we can see that the PCDs fibers are very evenly distributed and dense, with a diameter of about 300 nm; the fibers inside exhibit a 3D network interconnected structure. Figure 4The TEM image of a shows that there are large dark areas in the PAN fibers according to high-resolution TEM analysis. The elemental composition and distribution of the samples were analyzed by energy dispersive X-ray spectroscopy (EDX), and the uniformity of the distribution of FN-CDs nanoparticles was confirmed. Figure 4 The EDX image results in b show that the distribution of C, N, O, and F is relatively uniform, thus proving the uniform distribution of FN-CDs and demonstrating the successful preparation of the PCDs layer.

[0049] The Zn@PCDs obtained in this example were tested, and the test results are shown in Figure 5 ,from Figure 5 It can be seen that the thickness of the PCDs protective layer is about 20 μm.

[0050] Step S50, Zn@PCDs is used as the negative electrode of zinc ion battery, and its mechanism of action is shown in the following diagram: Figure 6 As shown in the figure, the surface of pure zinc produces a large number of dendrites and a series of side reactions during the cycle due to the uneven electric field distribution. Such as hydrogen evolution, corrosion, passivation, etc. However, due to the presence of a protective layer on the surface of the modified negative electrode, the growth of dendrites and the generation of side reactions are effectively suppressed. Therefore, a zinc ion symmetric battery was assembled using the same material as the counter electrode; a zinc ion half-cell was assembled using copper foil as the counter electrode; and a zinc ion full battery was assembled using MnO2 as the counter electrode. The performance of the battery was tested and compared with that of a battery without a negative electrode protective layer. The results are shown in the figure. Figure 7-8 As shown, from Figure 7 It can be seen that under different current density conditions, the rate performance of Zn@PCDs in this embodiment is better. Figure 8 It can be seen that under the conditions of different current densities, the cycle performance of Zn@PCDs in this embodiment is better.

[0051] Example 2

[0052] Step S10: dissolve 10 g of p-trifluoromethylbenzonitrile in 50 mL of 1 mol L -1 The mixture was then added to a sodium methoxide solution and stirred for 10 minutes until uniformly dispersed. Subsequently, 5 g of terephthalaldehyde was added to the mixture and sonicated for 10 minutes. The solvent was then transferred to an autoclave and hydrothermally reacted at 160°C for 2 hours. After cooling to room temperature, the mixture was diluted with 100 mL of deionized water and centrifuged at 10,000 rpm for 10 minutes with water and acetone, and the supernatant was removed. Finally, the FN-CDs material was dried in a vacuum oven at 80°C for 10 hours.

[0053] The FN-CDs material and PVDF powder obtained in this example were added to a beaker containing 2 mL of DMF solution at a mass ratio of 8:2, and magnetically stirred for 6 h to obtain a FN-CDs mixed slurry;

[0054] The FN-CDs mixed slurry obtained in this example was evenly coated on a zinc metal surface with a 5μm scraper for testing and characterization. The protective layer was approximately 2μm thick, the surface was flat and smooth, and the distribution of C, N, O, and F inside was relatively uniform, thus proving the successful preparation of the FN-CDs protective layer.

[0055] Electrochemical testing of the Zn@FN-CDs obtained in this example involved using the Zn@FN-CDs as the negative electrode in zinc-ion batteries. Symmetric zinc-ion cells were assembled using the same material as the counter electrode. A zinc-ion half-cell was assembled using copper foil as the counter electrode. Furthermore, a full zinc-ion cell was assembled using MnO2 as the counter electrode. The performance of these cells was tested and compared with that of a cell without a protective layer deposited on the negative electrode. The Zn@FN-CDs of this example demonstrated superior rate capability and cycling performance at various current densities.

[0056] Example 3

[0057] The carbon quantum dot material was prepared using the method of Example 1, except that:

[0058] In step S10, 5 g of trifluoromethylbenzonitrile was dissolved in 50 mL of 1 mol L -1 The mixture was then hydrothermally reacted in a sodium hydroxide solution and sonicated for 10 minutes until uniformly dispersed. Subsequently, 2 g of terephthalaldehyde was added to the mixture. The solvent was then transferred to an autoclave and hydrothermally reacted at 180°C for 2 hours. After cooling to room temperature, the mixture was diluted with 100 mL of deionized water and centrifuged at 10,000 rpm for 10 minutes with water and acetone, and the supernatant was removed. Finally, the carbon quantum dot material was dried in a vacuum oven at 80°C for 10 hours.

[0059] The carbon quantum dot material obtained in this example is light yellow and contains a large number of cyano and aldehyde groups, which can further regulate the orderly and uniform deposition of zinc ions on the surface of zinc metal.

[0060] Example 4

[0061] The carbon quantum dot protective layer material was prepared using the method of Example 1, except that:

[0062] In step S20, PAN powder and DMSO are mixed at a mass ratio of 1:9 to obtain a PAN spinning solution. The carbon quantum dot spinning solution obtained in this embodiment is more evenly dispersed, has stronger adhesion to the zinc metal surface, and is more stable during battery cycling.

[0063] Example 5

[0064] The carbon quantum dot material was prepared using the method of Example 2, except that:

[0065] In step S10, the mass ratio of trifluoromethylbenzonitrile to terephthalaldehyde is 3:1, and the obtained carbon quantum dot material has a higher proportion of cyano groups and F elements, which has a better effect on inducing 002 crystal surface modification of the zinc metal negative electrode.

[0066] The above are only preferred embodiments of the present application and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a modified zinc foil, characterized in that: include: PAN powder was mixed with DMF to obtain PAN spinning solution; dispersing the carbon quantum dot material in the PAN spinning solution to obtain a mixed spinning liquid; Spinning the mixed spinning liquid onto the surface of the zinc foil by electrospinning to obtain a modified zinc foil; The carbon quantum dot material has zinc-philic nucleation sites, and the preparation method of the carbon quantum dot material comprises: Terephthalaldehyde and p-trifluoromethylbenzonitrile are placed in a sodium methoxide solution for hydrothermal reaction to obtain a carbon quantum dot material.

2. The method for preparing the modified zinc foil according to claim 1, wherein The mass ratio of the terephthalaldehyde to the trifluoromethylbenzonitrile is 1:1-2.

3. The method for preparing the modified zinc foil according to claim 1, wherein: The temperature of the hydrothermal reaction is 120-180° C., and the time is 1-5 hours.

4. The method for preparing the modified zinc foil according to claim 1, wherein: The sodium methoxide concentration is 0.5-1.5 mol L -1 .

5. The method for preparing the modified zinc foil according to claim 1, wherein: The mass ratio of the PAN powder to the DMF is 0.5-1:9, and the ratio of the carbon quantum dot material to the PAN spinning solution is 0.5-1:

10.

6. The method for preparing the modified zinc foil according to claim 5, wherein: The electrospinning process specifically includes: pouring the mixed spinning liquid into a syringe, wrapping the zinc foil on the surface of the receiving device, and performing directional spinning at 45-60 degrees to the receiving device; the electrospinning speed is 0.5-2 mL h -1 , the drying time is 4-8 h.

7. A modified zinc foil, characterized in that: The modified zinc foil is obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the modified zinc foil according to claim 7 as a negative electrode material for a zinc ion battery.

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