阅读说明：本技术 硝酸盐辅助合成掺氮纳米碳片及其储钠应用 (Nitrate-assisted synthesized nitrogen-doped nano carbon sheet and sodium storage application thereof ) 是由 王焕磊 董光河 于 2018-05-29 设计创作，主要内容包括：本发明公开了一种利用硝酸盐来辅助合成掺氮纳米碳片材料的方法。该方法是利用红藻类植物提取物-卡拉胶为前驱体,以碱金属硝酸盐(LiNO<Sub>3</Sub>,NaNO<Sub>3</Sub>,KNO<Sub>3</Sub>,RbNO<Sub>3</Sub>,CsNO<Sub>3</Sub>)为活化剂和氮源,经高温煅烧实现。首先将卡拉胶在高温条件下溶解于去离子水中,然后加入一定量的碱金属硝酸盐水溶液,充分混合后自然冷却至室温形成胶体,再进行冷冻干燥彻底除去水分,这样就得到了卡拉胶-碱金属硝酸盐前驱体。将上述前驱体放入到管式炉中,在惰性气体保护下以一定升温速率升温至最优温度并保温一定时间进行碳化,再经过酸洗、水洗、干燥就能得到氮掺杂多孔纳米碳片。该方法通过控制工艺条件实现了对碳微观形貌和元素含量等进行调控,得到具有片层结构和大比表面积以及丰富的氮元素掺杂的碳,可用于储钠电极材料。(the invention discloses a method for synthesizing a nitrogen-doped nano carbon sheet material by using nitrate as an auxiliary material. The method is realized by taking carrageenan which is a red algae plant extract as a precursor, taking alkali metal nitrate (LiNO 3, NaNO3, KNO3, RbNO3 and CsNO 3) as an activating agent and a nitrogen source and calcining at high temperature. Firstly, dissolving carrageenan in deionized water at high temperature, then adding a certain amount of alkali metal nitrate aqueous solution, fully mixing, naturally cooling to room temperature to form colloid, and then carrying out freeze drying to thoroughly remove moisture, thus obtaining the carrageenan-alkali metal nitrate precursor. And putting the precursor into a tubular furnace, heating to an optimal temperature at a certain heating rate under the protection of inert gas, preserving heat for a certain time for carbonization, and carrying out acid pickling, washing and drying to obtain the nitrogen-doped porous nano carbon sheet. The method realizes the regulation and control of carbon micro-morphology, element content and the like by controlling process conditions, obtains the nitrogen-doped carbon with a lamellar structure, a large specific surface area and abundant nitrogen elements, and can be used for sodium storage electrode materials.)

1. the nitrate-assisted method for synthesizing the nitrogen-doped nano carbon sheet is characterized by comprising the following steps of:

(1) Mixing, namely adding hydrophilic carrageenan powder extracted from red algae plants into hot water of 80 ℃, stirring until the carrageenan is completely dissolved, adding a solution in which a metal nitrate activator is dissolved, continuously stirring for a certain time, and naturally cooling to room temperature to form colloid; (2) drying, namely freeze-drying the colloid for a period of time to completely remove water; (3) carbonizing, namely putting the dried sample into a tubular furnace, heating to an optimal temperature at a certain heating rate under the protection of inert gas, and keeping for a certain time to fully carbonize and activate the sample; (4) cleaning: and stirring the activated sample in 200ml of 2M diluted hydrochloric acid for 24 hours, then carrying out suction filtration by using a large amount of deionized water until the sample is neutral, and drying the sample in an oven at the temperature of 80 ℃ to obtain the nitrogen-doped porous nano carbon sheet.

k i λ2. The method for synthesizing the nitrogen-doped nanocarbon plate with the assistance of the nitrate as recited in claim 1, wherein: in the step (1), the precursor of the red algae plant extract is as follows: k-carrageenan, i-carrageenan, lambda-carrageenan and the like, wherein the activating agent and the nitrogen source are both prepared in the step (1): and alkali metal nitrates such as LiNO3, NaNO3, KNO3, RbNO3 and CsNO3 are regulated and controlled, and the mass ratio of the precursor to the activator is 10: 1-1: 1.

3. The method for synthesizing the nitrogen-doped nanocarbon plate with the assistance of the nitrate as recited in claim 1, wherein: in the step (3), the temperature of carbonization and activation is 400-1200 ℃, the heating rate is 1-10 ℃ for min-1, and the heat preservation time is 0-8 h.

4. the method for synthesizing the nitrogen-doped nano carbon sheet with the assistance of the nitrate according to the claims 1 to 3, which is characterized in that nitrogen atom introduction and high-temperature activation are synchronously carried out, and finally the high-nitrogen-doped nano carbon sheet is obtained.

5. The method for synthesizing the nitrogen-doped nano carbon sheet assisted by the nitrate as recited in claims 1 to 4, characterized in that the nitrogen-doped nano carbon sheet material can be applied to electrode materials of sodium ion batteries and mixed sodium ion capacitors.

Technical Field

The invention belongs to the field of electrochemical energy storage, and provides a method for simultaneously introducing nitrogen atoms into the surface of carbon and modifying the microscopic morphology of the carbon to prepare a nitrogen-doped nano carbon sheet, and application of the nitrogen-doped nano carbon sheet as a negative electrode material of a sodium ion battery and a mixed sodium ion capacitor.

Background

Due to severe environmental pollution caused by the overuse of coal and oil and the increasing global energy consumption, energy storage devices having both high energy density and high power density have attracted much attention. Currently, lithium ion batteries are the primary energy storage devices due to their advantages of high energy density and high operating voltage. However, due to the use of a large amount of lithium ion batteries, lithium resources in the world face the current situation of gradual depletion, and energy storage devices rich in resources are urgently needed to be found.

Because sodium in nature has abundant resources, wide distribution and low price, an energy storage device based on sodium ions becomes one of important candidates of an energy storage system. Energy storage devices based on sodium ions mainly include sodium ion batteries and hybrid sodium ion capacitors. Sodium ion batteries, like lithium ion batteries, have a very high energy density, but a low power density. To compensate for this drawback, hybrid sodium ion capacitors with both high energy density and high power density have been developed. A hybrid sodium ion capacitor, i.e., a device employing a capacitor-type positive electrode and a battery-type negative electrode. In such a hybrid capacitor, charge enters the negative electrode by intercalation, similar to a battery; meanwhile, charges enter the anode through reversible adsorption, and the adsorption is beneficial to improving the rate performance compared with insertion, similar to a super capacitor. Because the specific capacity of the negative electrode is obviously larger than that of the positive electrode, the mass ratio of the active substances of the positive electrode and the negative electrode needs to be regulated and controlled to realize the maximum energy density of the device. The invention realizes the highest energy density of the sodium ion capacitor by fixing the loading capacity of the cathode active material and changing the loading capacity of the anode active material to find the optimal mass ratio of the anode active material and the cathode active material.

electrode materials are the most important part of energy storage devices, and mainly comprise carbon materials, metal oxides, alloys, metal sulfides and the like. Carbon materials have low cost, high conductivity and cycling stability, and have become the main electrode materials of energy storage devices at present. In the carbon material, the high specific surface area, the hierarchical pore structure and the lamellar graphene structure can be beneficial to the transmission and adsorption of electrolyte ions, so that high electrochemical performance is obtained. In addition, heterogeneous heteroatoms such as nitrogen, sulfur, phosphorus and other elements introduced into the carbon material can generate defects on the surface of the carbon material, and the defects and electrolyte ions generate oxidation-reduction reaction, so that the electrochemical energy storage capacity of the carbon material is greatly improved. Suitable precursors and activators are of utmost importance in order to obtain heteroatom-doped porous sheet carbon materials. According to the invention, the alkali metal nitrate is used as an activating agent and a nitrogen source, so that the morphology of the carbon material is regulated, and the nitrogen atoms are introduced into the carbon skeleton, thereby realizing excellent sodium storage performance.

Disclosure of Invention

The invention aims to obtain a nitrogen-doped carbon material with a higher specific surface area and a sheet structure by a nitrate-assisted synthesis method, wherein the nitrogen-doped carbon material adopts carrageenan which is an extract of marine organism red algae as a raw material, the prepared carbon material has excellent electrochemical performance, and the carbon material is applied to a sodium ion battery and a mixed sodium ion capacitor to achieve the highest energy density by adjusting the mass ratio of active substances of a positive electrode and a negative electrode of the sodium ion capacitor.

the technical scheme adopted by the invention for solving the technical problem is as follows:

(1) Adding a certain amount of carrageenan powder into deionized water with the mass of 40 times, completely dissolving in an oil bath at 80 ℃, keeping the temperature constant, and adding a certain amount of alkali metal nitrate activator aqueous solution, wherein the mass ratio of the carrageenan to the activator is 10: 1-1: 1. Fully stirring to uniformly mix the carrageenan solution and the activator solution, naturally cooling to room temperature to form a carrageenan-alkali metal nitrate colloid, and then putting the colloid into a freeze dryer for drying so as to completely remove moisture, thereby obtaining a substance labeled crop material A;

(2) and moving the material A into a tubular furnace, heating to 400-1200 ℃ at a heating rate of 3 ℃/min under the protection of inert gas, and preserving heat for 0-8 h to ensure that the material A is fully carbonized and activated and the introduction of nitrogen element is completed. Continuously stirring the carbonized and activated sample in 2mol/L diluted hydrochloric acid for 24 hours to remove impurities, then carrying out suction filtration by using a large amount of deionized water, drying the sample, and then recording the dried sample as a material B;

(3) the material B is applied to electrode materials of a sodium ion battery and a mixed sodium ion capacitor, and the maximized energy density is obtained by adjusting the mass ratio of the positive electrode active substance to the negative electrode active substance of the sodium ion capacitor.

compared with the prior art, the invention has the beneficial effects that:

(1) the invention uses the extract of the marine organism-red algae as the raw material, has wide source and is beneficial to large-scale preparation. Meanwhile, the carrageenan contains a small amount of sulfur element, so that the self-doping of hetero atoms is realized. In addition, the unique double-helix structure characteristic of the carrageenan determines that the carrageenan is beneficial to element doping during carbonization;

(2) The invention uses alkali metal nitrate as an activator, and the alkali metal nitrate also plays a role of a nitrogen source. Under the action of alkali metal nitrate, carrageenan is carbonized and activated at high temperature to obtain the porous flaky nanocarbon appearance, and meanwhile, a large amount of nitrogen elements are successfully introduced to be matched with sulfur elements contained in the carrageenan, so that the electrochemical performance of the carrageenan is improved;

(3) The prepared nitrogen-doped nano carbon sheet is applied to electrode materials of sodium ion batteries and mixed sodium ion capacitors, and the sheet porous structure of the nitrogen-doped nano carbon sheet is beneficial to the rapid transmission of electrolyte, so that the nitrogen-doped nano carbon sheet shows high specific capacity and excellent rate capability when applied to electrodes of the sodium ion batteries. The introduced nitrogen element and the internal sulfur element are subjected to redox reaction with sodium ions to generate pseudo capacitance, so that the sodium ion battery has higher specific capacity. In addition, the quality of the anode of the mixed sodium ion capacitor is regulated and controlled, so that a device with high energy density and power density is obtained.

Drawings

fig. 1 is a Scanning Electron Microscope (SEM) photograph of the nitrogen-doped nanocarbon plate of example 1.

Fig. 2 is a Scanning Electron Microscope (SEM) photograph of the nitrogen-doped nanocarbon plate of example 2.

FIG. 3 is a Scanning Electron Microscope (SEM) photograph of the nitrogen-doped nanocarbon plate of example 3.

FIG. 4 is a Transmission Electron Microscope (TEM) photograph of the nitrogen-doped nanocarbon plate of example 1.

FIG. 5 is a Transmission Electron Microscope (TEM) photograph of the nitrogen-doped nanocarbon plate of example 2.

FIG. 6 is a Transmission Electron Microscope (TEM) photograph of a nitrogen-doped nanocarbon plate of example 3.

fig. 7 is a capacity plot for the assembled sodium ion battery of example 4 at different current densities.

figure 8 is a graph of the performance of the assembled sodium ion battery of example 4 at a current density of 2A g-1 for 500 cycles.

FIG. 9 is a plot of cyclic voltammograms of the assembled hybrid sodium ion capacitor of example 5 at a scan rate of 10 mV/s.

FIG. 10 is a constant current charge and discharge plot of the assembled hybrid sodium ion capacitor of example 5 at a current density of 1A g-1.

Figure 11 is a graph of energy density versus power density for different current densities for the assembled hybrid sodium ion capacitor of example 5.

Detailed Description

the present invention is illustrated by way of the following specific examples, which are not intended to be limiting.