Preparation method of zinc-rich seed-containing carbon nanofibers for negative electrode material of aqueous zinc-ion battery

Abstract

The present invention discloses a preparation method of zinc-seed-rich carbon nanofibers for the negative electrode material of an aqueous zinc-ion battery. First, bacterial cellulose is oxidized, then soaked in a zinc nitrate Zn(NO3)2 solution to adsorb zinc ions, and then annealed to obtain zinc-seed-rich carbon nanofibers. The preparation process of the negative electrode material of the present invention is simple and low-cost, has ultra-long cycle stability and high energy density, and helps to promote the development and application of advanced flexible electrochemical energy storage devices.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for aqueous zinc-ion batteries, and particularly to a preparation method of zinc-seed-rich carbon nanofibers for use as negative electrode materials for aqueous zinc-ion batteries. Background Art

[0002] The increasing energy demand and deteriorating environmental problems indicate that the sustainable development of new energy is imperative. Rechargeable batteries with high charge-discharge efficiency, long cycle life, large power and energy density, pollution-free operation and low maintenance cost can meet the demand for clean energy storage. Lithium-ion batteries have high energy density and long cycle life, which have promoted the booming development in the fields of smart portable devices and electric vehicles. However, the safety hazards of lithium batteries, the scarcity of lithium resources and the continuously rising price of lithium ore have hindered the further application of lithium-ion batteries. Zinc-ion batteries show very broad prospects in large-scale electrochemical energy storage applications due to many advantages such as high volume specific capacity, simple preparation process, safety, environmental friendliness and rich resources.

[0003] Currently, the negative electrode materials for aqueous zinc-ion batteries mainly include alloy materials, three-dimensional metal scaffold materials and carbonaceous materials. In contrast, carbonaceous materials have relatively excellent electrical conductivity, natural abundance, controllable microstructure and remarkable physical and chemical stability, and are one of the most favorable anode materials for aqueous zinc-ion batteries. However, due to the high energy barrier of zinc nucleation, it is difficult for pure carbon materials to obtain uniform zinc deposition, which seriously affects the reversibility of aqueous zinc-ion batteries. The carbonaceous materials can reduce the zinc nucleation overpotential through metal element anchoring or heteroatom doping, but the energy density of the battery is reduced. At the same time, the preparation of carbonaceous materials such as carbon nanofibers and carbon nanotubes reported requires harsh synthesis conditions and complex process flows, which severely limits their practical applications. Summary of the Invention

[0004] Aiming at the above problems existing in aqueous zinc-ion batteries at present, the present invention provides a preparation method of zinc-seed-rich carbon nanofibers for use as negative electrode materials for aqueous zinc-ion batteries. The negative electrode material prepared by this method has excellent structural stability, high energy density, long cycle life and excellent cost-effectiveness, and is suitable for large-scale electrochemical energy storage systems.

[0005] The present invention adopts the following technical solutions to achieve the purpose:

[0006] A preparation method of zinc-seed-rich carbon nanofibers for use as negative electrode materials for aqueous zinc-ion batteries, comprising the following steps:

[0007] Step 1: Dissolve 2,2,6,6-tetramethylpiperidine-1-oxyl radical TEMPO and sodium bromide NaBr in deionized water to obtain a mixed solution; add freeze-dried bacterial cellulose to the mixed solution, then add sodium hypochlorite NaClO solution for oxidation, and continuously adjust the pH of the system with sodium hydroxide NaOH solution during the oxidation process; wash the obtained product with deionized water, filter, and freeze-dry to obtain oxidized bacterial cellulose;

[0008] Step 2: Dissolve zinc nitrate in deionized water to obtain a zinc nitrate solution; add the oxidized bacterial cellulose obtained in Step 1 to the zinc nitrate Zn(NO3)2 solution and stir; wash the obtained product with deionized water, filter, and freeze-dry to obtain oxidized bacterial cellulose adsorbed with zinc ions;

[0009] Step 3: Heat-treat the oxidized bacterial cellulose adsorbed with zinc ions obtained in Step 2 in a nitrogen atmosphere. After natural cooling to room temperature, carbon nanofibers rich in zinc seeds for the negative electrode material of an aqueous zinc ion battery are obtained, denoted as CNF-Zn.

[0010] Preferably, in Step 1, the concentration of the sodium hypochlorite solution is 6-14 wt%, and the dosage ratio of TEMPO, sodium bromide, bacterial cellulose, deionized water, and sodium hypochlorite solution is 0.06-0.07 g: 0.30-0.50 g: 3.00-5.00 g: 350-450 mL: 35-45 mL.

[0011] Preferably, in Step 1, adjust the pH of the system to 9.5-10.5.

[0012] Preferably, in Step 1, the oxidation time is 1.5-3 h.

[0013] Preferably, in Step 2, the dosage ratio of oxidized bacterial cellulose, zinc nitrate, and deionized water (the deionized water used to prepare the zinc nitrate solution) is 0.20-0.30 g: 0.035-0.045 g: 90-110 mL.

[0014] Preferably, in Step 2, the stirring time is 20-30 h.

[0015] Preferably, in Step 3, the heat treatment temperature is 500-1000 °C, the heat treatment time is 2-4 h, and the heating rate is 1-3 °C / min -1 。

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] After adsorbing zinc ions by oxidized bacterial cellulose, the present invention further prepares a lightweight flexible three-dimensional carbon fiber material rich in uniform zinc seeds through annealing treatment. The three-dimensional carbon fiber structure with a porous interconnected network significantly reduces the local current density and alleviates the volume change of the material during charge and discharge. The zinc seeds provide uniform nucleation sites, thus having excellent rate performance and cycle stability. The preparation method of the present invention is simple and low-cost, and the obtained negative electrode material has ultra-long cycle stability and high energy density, which helps to promote the development and application of advanced flexible electrochemical energy storage devices. Brief Description of the Drawings

[0018] Figure 1 is a flow chart of the preparation method of the carbon nanofibers rich in zinc seeds of the present invention;

[0019] Figure 2 is a scanning electron microscope image of CNF-Zn prepared in Example 1 of the present invention;

[0020] Figure 3 is a high-resolution transmission electron microscope image of CNF-Zn prepared in Example 1 of the present invention;

[0021] Figure 4 is an elemental distribution map of CNF-Zn prepared in Example 1 of the present invention;

[0022] Figure 5 is an X-ray diffraction pattern of CNF-Zn prepared in Example 1 of the present invention;

[0023] Figure 6 is an X-ray photoelectron spectrum of CNF-Zn prepared in Example 1 of the present invention;

[0024] Figure 7 is a cyclic voltammogram of a full cell assembled with CNF-Zn prepared in Example 1 of the present invention;

[0025] Figure 8 is a nucleation overpotential diagram of half cells assembled with CNF-Zn prepared in Example 1 of the present invention and CNF prepared in Comparative Example 1 respectively;

[0026] Figure 9 is an electrochemical impedance spectrum diagram of half cells assembled with CNF-Zn prepared in Example 1 of the present invention and CNF prepared in Comparative Example 1 respectively;

[0027] Figure 10 is a scanning electron microscope image of the electrodes after cycling of half cells assembled with CNF-Zn prepared in Example 1 of the present invention and CNF prepared in Comparative Example 1 respectively;

[0028] Figure 11 is a charge-discharge curve diagram of full cells assembled with CNF-Zn prepared in Example 1 of the present invention and CNF prepared in Comparative Example 1 respectively;

[0029] Figure 12 Cycling performance graphs of all-solid-state batteries assembled with CNF-Zn prepared in Example 1 of the present invention and CNF prepared in Comparative Example 1, respectively;

[0030] Figure 13 Rate performance graphs of all-solid-state batteries assembled with CNF-Zn prepared in Example 1 of the present invention and CNF prepared in Comparative Example 1, respectively. Detailed implementation manners

[0031] To further illustrate the present invention, the following describes in detail a preparation method of a negative electrode material with a carbon nanofiber structure rich in zinc seeds for a novel high-performance aqueous zinc-ion battery provided by the present invention in combination with examples, and is illustrated in conjunction with the accompanying drawings, but it should not be construed as a limitation to the protection scope of the present invention.

[0032] Example 1

[0033] The carbon nanofibers rich in zinc seeds are prepared in the following steps in this example:

[0034] Step 1: Dissolve 0.064 g of TEMPO and 0.40 g of sodium bromide in 400 mL of deionized water to obtain a mixed solution; add 4.00 g of freeze-dried bacterial cellulose to the above mixed solution, then add 40 mL of a 10 wt% sodium hypochlorite solution, oxidize for 2 h, and continuously adjust the pH of the system to 10 with sodium hydroxide solution during the oxidation process; the obtained product is washed with deionized water, filtered, and freeze-dried for 3 days to obtain oxidized bacterial cellulose.

[0035] Step 2: Dissolve 0.038 g of zinc nitrate in 100 mL of deionized water, then add 0.25 g of oxidized bacterial cellulose to the zinc nitrate solution and stir for 24 h; the obtained product is rinsed with deionized water, filtered, and freeze-dried for 3 days to obtain oxidized bacterial cellulose adsorbed with zinc ions.

[0036] Step 3: Place the oxidized bacterial cellulose adsorbed with zinc ions in a tubular furnace under a nitrogen atmosphere at 700 °C for 2 h, and the heating rate of the tubular furnace is 2 °C / min -1 . After natural cooling to room temperature, carbon nanofibers rich in zinc seeds are obtained, denoted as CNF-Zn.

[0037] It can be seen from Figure 1 that through simple chemical adsorption and annealing processes, the zinc seeds are attached to the carbon nanofibers after the oxidation treatment of the bacterial cellulose.

[0038] Figure 2 This is the scanning electron microscope image of the CNF-Zn obtained in this example, and it can be clearly observed that the sample can still maintain a three-dimensional porous interconnected network structure after multiple steps of treatment.

[0039] Figure 3 This is the high-resolution transmission electron microscopy image of CNF-Zn obtained in this example. The carbon nanofibers have amorphous characteristics.

[0040] Figure 4 This is the elemental distribution map of CNF-Zn obtained in this example. It can be seen from the left figure that the distributions of C, O, and Zn elements are uniform, and it can be clearly distinguished from the right figure that zinc elements are uniformly attached to the carbon nanofibers.

[0041] Figure 5 This is the X-ray diffraction pattern of CNF-Zn obtained in this example. The main body of the carbon nanofibers is an amorphous carbon material and there are no impurity peaks.

[0042] Figure 6 This is the X-ray photoelectron spectrum of CNF-Zn obtained in this example. The spin-orbit peaks of 2p 1 / 2 and 2p 3 / 2 of zinc are fitted. At the same time, combining Figure 4 , Figure 5 it can be shown that the zinc species are not sintered into zinc oxide and have not evaporated and disappeared.

[0043] A half-cell is assembled using CNF-Zn obtained in this example as the positive electrode, zinc foil as the negative electrode, glass fiber as the separator, and 2M ZnSO4 solution as the electrolyte. After the half-cell is subjected to constant current discharge deposition of 10 mAh cm -2 of zinc, the positive electrode is taken out and denoted as CNF-Zn@Zn. A full cell is assembled using CNF-Zn@Zn as the negative electrode, sodium vanadate coated on a stainless steel mesh as the positive electrode, glass fiber as the separator, and 2M ZnSO4 solution as the electrolyte. The above half-cell and full cell are both button cells.

[0044] The cyclic voltammetry curve test of the full cell is carried out on a CHI760E electrochemical workstation. Figure 7 This is the cyclic voltammogram of CNF-Zn prepared in this example. It can be observed that relatively overlapping oxidation and reduction peaks indicate that the material has excellent reversibility.

[0045] Comparative Example 1

[0046] In this example, carbon nanofibers without zinc seeds are prepared according to the following steps:

[0047] Step 1: Dissolve 0.064 g of TEMPO and 0.40 g of sodium bromide in 400 mL of deionized water to obtain a mixed solution; add 4.00 g of freeze-dried bacterial cellulose to the above mixed solution, then add 40 mL of a 10 wt% sodium hypochlorite solution, oxidize for 2 h, and continuously adjust the pH of the system to 10 with sodium hydroxide solution during the oxidation process; wash the obtained product with deionized water, filter, and freeze-dry for 3 days to obtain oxidized bacterial cellulose.

[0048] Step 2: Place the oxidized bacterial cellulose in a tubular furnace under a nitrogen atmosphere at 700 °C for 2 h, and the heating rate of the tubular furnace is 2 °C min -1 . After natural cooling to room temperature, carbon nanofibers without zinc seeds are obtained, denoted as CNF.

[0049] Assemble the battery with the CNF of this comparative example in the same method as in Example 1.

[0050] Figure 8 is the nucleation overpotential diagram of the samples obtained in Example 1 and Comparative Example 1. The nucleation overpotentials of CNF-Zn and CNF are 12 mV and 21 mV respectively, further verifying that zinc seeds are more beneficial to the uniform deposition of zinc.

[0051] Figure 9 is the electrochemical impedance spectroscopy diagram of the samples obtained in Example 1 and Comparative Example 1. Compared with CNF, the CNF-Zn material shows a smaller charge transfer resistance, so its electrochemical performance is more excellent.

[0052] Figure 10 (a) and Figure 10 (b) are the scanning electron microscope images of the electrodes of the samples obtained in Example 1 and Comparative Example 1 after cycling 20, 50, and 100 times at a current density of 2 mA cm -2 . It can be seen that the CNF-Zn electrode still maintains a flat and dense deposition morphology after 100 cycles; in contrast, the morphology of CNF gradually fluctuates and breaks.

[0053] Figure 11 is the charge-discharge curve diagram of the samples obtained in Example 1 and Comparative Example 1 at 1.0 A g -1 . The voltage gap of CNF-Zn is smaller than that of CNF, indicating that the polarization rate of the material rich in zinc seeds is lower.

[0054] Figure 12 is the cycling performance of the samples obtained in Example 1 and Comparative Example 1 at 2.0 A g -1 . The capacity of CNF-Zn still remains at a high value of 130.2 mAh g after 300 cycles; however, serious capacity decay is observed for CNF after 15 and 225 cycles respectively. -1

[0055] Figure 13 It is the rate performance graph of the samples obtained in Example 1 and Comparative Example 1. The specific capacities of two materials, CNF-Zn and CNF, were tested at the current densities of 1.0, 2.0, 4.0, 6.0, and 10.0 Ag -1 respectively. It can be seen from the graph that with the increase of the charge-discharge rate, the CNF-Zn material shows a smaller capacity decay, and when the current density returns to 1.0 Ag -1 the capacity can also recover quickly. In contrast, the capacity decay of the CNF material is more severe, showing extremely low capacity at high currents.

[0056] The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of zinc-rich seed-containing carbon nanofibers for the negative electrode material of an aqueous zinc ion battery, characterized in that, It includes the following steps: Step 1: Dissolve TEMPO and sodium bromide in deionized water to obtain a mixed solution; add the freeze-dried bacterial cellulose into the mixed solution, then add sodium hypochlorite solution, carry out oxidation, and continuously adjust the pH of the system with sodium hydroxide solution during the oxidation process; wash the obtained product with deionized water, then filter and freeze-dry to obtain oxidized bacterial cellulose; Step 2: Dissolve zinc nitrate in deionized water to obtain a zinc nitrate solution; add the oxidized bacterial cellulose obtained in Step 1 into the zinc nitrate solution and stir; wash the obtained product with deionized water, then filter and freeze-dry to obtain oxidized bacterial cellulose adsorbed with zinc ions; Step 3: Carry out heat treatment on the oxidized bacterial cellulose adsorbed with zinc ions obtained in Step 2 in a nitrogen atmosphere, the heat treatment temperature is 500 - 700 °C, and after naturally cooling to room temperature, carbon nanofibers rich in zinc seeds for the negative electrode material of an aqueous zinc ion battery are obtained.

2. The preparation method according to claim 1, wherein: In Step 1, the concentration of the sodium hypochlorite solution is 6 - 14 wt%, and the dosage ratio of TEMPO, sodium bromide, bacterial cellulose, deionized water and sodium hypochlorite solution is 0.06 - 0.07 g: 0.30 - 0.50 g: 3.00 - 5.00 g: 350 - 450 mL: 35 - 45 mL.

3. The preparation method according to claim 1, characterized in that: In Step 1, adjust the pH of the system to 9.5 - 10.

5.

4. The preparation method according to claim 1, characterized in that: In Step 1, the oxidation time is 1.5 - 3 h.

5. The preparation method according to claim 1, characterized in that: In Step 2, the dosage ratio of oxidized bacterial cellulose, zinc nitrate and deionized water is 0.20 - 0.30 g: 0.035 - 0.045 g: 90 - 110 mL.

6. The preparation method according to claim 1, characterized in that: In Step 2, the stirring time is 20 - 30 h.

7. The preparation method according to claim 1, characterized in that: In Step 3, the time of the heat treatment is 2 to 4 h, and the heating rate is 1 to 3 °C / min -1 .

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