Preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature

Abstract

The invention discloses a preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature, and belongs to the technical field of battery material preparation. The method is suitable for biomass precursors of various sources, various waste biomass can be efficiently converted into high-performance pulse hard carbon materials, and stable improvement of product quality and performance is achieved. Compared with a traditional carbonization process, the transient high-temperature preparation process disclosed by the invention has the advantages that second-level rapid carbonization can be realized, energy and time are remarkably saved, and low-value waste biomass is converted into a high-performance hard carbon material; compared with the traditional hard carbon material, the pulse hard carbon prepared by the invention shows higher reversible capacity, better rate capability and cycling stability when applied to the negative electrode of the sodium-ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery material preparation, and particularly relates to a preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature. BACKGROUND

[0002] Under the background of accelerating global energy transformation, rechargeable battery technology has become the core of the energy storage field. Among them, lithium ion batteries are considered as the most potential choice in the field of electronic devices and electric vehicles due to their high energy density and excellent cycle performance. However, the shortage and uneven distribution of lithium resources seriously restrict the development of lithium ion batteries. Sodium ion batteries, as an important alternative to lithium ion batteries, have attracted widespread attention due to their unique advantages such as resource abundance, electrochemical similarity and safety. The core challenge facing the commercialization of sodium ion batteries lies in the choice of negative electrode materials. Because the radius of sodium ion is larger than that of lithium ion, the traditional graphite negative electrode cannot provide a stable sodium storage structure. Hard carbon material can realize efficient sodium ion intercalation / adsorption due to its expanded interlayer spacing, abundant defect sites and microporous structure, and has become the most promising solution for sodium battery negative electrode.

[0003] At the same time, billions of tons of agricultural waste are facing the dilemma of incineration and landfill every year, not only releasing greenhouse gases, but also causing resource waste. These wastes contain rich cellulose, hemicellulose and lignin, which are natural carbon precursor resources. For example, the cellulose content in bamboo is as high as 40-50%, and its value can be increased by nearly ten times after carbonization. Converting waste biomass into high-performance hard carbon materials has significant economic and environmental benefits. Biomass precursors are almost cost-free, and the growth process of biomass fixes carbon, and the conversion of waste realizes a "negative carbon closed loop".

[0004] The traditional hard carbon preparation method is carried out by two-step carbonization method: (1) low-temperature pyrolysis (about 700℃) to produce biochar, (2) high-temperature carbonization (such as 1400-1500℃, heating time >2 hours) to convert biochar into hard carbon material. Simple pyrolysis will lead to immature microstructure and poor performance of hard carbon (<200 mAh / g). After long-time high-temperature carbonization, hard carbon presents a complex microstructure, including randomly oriented graphite crystallites, amorphous regions and nanopores, resulting in different microstructures and performances of different biomass-based hard carbon. For example, wood and bamboo have rigid, lignin-containing frameworks, which tend to produce carbon materials with strong, layered pore systems; in contrast, cotton has high crystallinity and high cellulose content, which tends to form ordered graphite domains. In addition, the traditional carbonization method leads to complex evolution of various structural parameters (such as graphite crystallite size, interlayer spacing and porosity), which cannot be accurately controlled, making it a great challenge to elucidate the structure-performance relationship. SUMMARY

[0005] The main purpose of the present application is to provide a preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature, which can realize optimization of performance of different biomass-derived hard carbon, is efficient, rapid, high-yield and environment-friendly, and has good application prospect.

[0006] The first purpose of the present application is to provide a preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature, which comprises the following steps: first, pre-carbonization treatment of biomass precursor under inert atmosphere, then natural cooling to room temperature to form biochar; then loading the biochar on carbon cloth, and rapid heating and rapid cooling heat treatment of the carbon cloth by using transient high temperature heating method to obtain pulse hard carbon.

[0007] The present application induces carbonization of the material in ultra-short heating time after pre-carbonization treatment of the biomass precursor, and rapidly cools down, i.e. pulse hard carbon is obtained.

[0008] Preferably, the biomass precursor is at least one of cotton, peanut shell and glucose.

[0009] Preferably, the inert atmosphere is at least one of argon, helium and nitrogen.

[0010] Preferably, the pre-carbonization treatment temperature is 600-900 DEG C, and it can be understood that the above pre-carbonization treatment temperature can be 600 DEG C, 700 DEG C, 800 DEG C or 900 DEG C; the treatment time is 1-2h, and similarly, the treatment time can be 1h, 1.5h or 2h; but it is not limited to the listed values, and other values not listed in the value range are also applicable.

[0011] Preferably, the transient high temperature heating temperature is 1000-2000 DEG C, and the heating time is 10-60s.

[0012] Preferably, the transient high temperature heating method is heating by using Joule heat generated by constant current power supply or constant voltage power supply; the output current of the constant current power supply is 1-60A; the output voltage range of the constant voltage power supply is 10-200V; and the heating time is greater than or equal to 5ms.

[0013] Preferably, the rapid heating speed is 10 2 -10 5 DEG C / s.

[0014] Preferably, the rapid cooling speed is 10-10 3 DEG C / s; and the rapid cooling method is at least one of natural cooling, air cooling and water cooling.

[0015] The second object of the present application is to propose a pulse hard carbon prepared by a preparation process for realizing high-value conversion of waste biomass into hard carbon material based on transient high temperature.

[0016] The second object of the present application is to propose the application of the above pulse hard carbon in the preparation of sodium ion battery or lithium ion battery materials.

[0017] The beneficial effects of the present application over the prior art are: (1) The present application provides a preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature, which uses programmable Joule heating technology to convert biomass precursors of different sources into hard carbon with excellent performance at low cost and intelligently, and is suitable for biomass precursors of various sources, can efficiently convert various waste biomass into high-performance hard carbon material, and realizes stable improvement of product quality and performance, providing a practical solution for high-value conversion of waste biomass on an industrial scale; (2) Compared with traditional carbonization processes, the transient high temperature preparation process of the present application can realize rapid carbonization in seconds, significantly saving energy and time, and converting low-value waste biomass into high-performance hard carbon material; (3) Compared with traditional hard carbon materials, the pulse hard carbon prepared by the present application exhibits higher reversible capacity, better rate performance and cycle stability in the application of sodium ion battery negative electrode; (4) Compared with traditional long-time high-temperature carbonization processes, the present application only needs transient (second-level) electric heating to complete the carbonization of biomass, greatly improving the energy utilization efficiency; (5) The pulse hard carbon prepared by the present application through transient high temperature has good graphite microcrystalline structure, because the precise controllable temperature and time of transient high temperature can freeze carbon atoms at appropriate positions; (6) Compared with traditional hard carbon materials, the pulse hard carbon prepared by the present application through transient high temperature has greater crystallinity and rich pore structure. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description only represent some embodiments of the present application, and other related drawings can also be obtained by those skilled in the art without creative labor.

[0019] Figure 1 Scanning electron microscope images of the biochar, pulse hard carbon obtained from Example 1 and traditional hard carbon obtained from Comparative Example 1 of the present application; Figure 2High-resolution transmission electron microscopy images of the biochar and pulse hard carbon obtained in Example 1 of the present invention and the traditional hard carbon obtained in Comparative Example 1; Figure 3 The Raman spectra of the biochar and pulse hard carbon obtained in Example 1 of the present invention and the traditional hard carbon obtained in Comparative Example 1 are shown; Figure 4 Comparison of the capacity and cost of the biochar and pulse hard carbon obtained in Example 1 of the present invention and the traditional hard carbon obtained in Comparative Example 1; Figure 5 The first week charge and discharge curves of the biochar and pulse hard carbon obtained in Example 1 of the present invention and the traditional hard carbon obtained in Comparative Example 1; Figure 6 X-ray diffraction patterns of the biochar and pulse hard carbon obtained in Example 1 of the present invention and the traditional hard carbon obtained in Comparative Example 1; Figure 7 This is a performance optimization result diagram of pulse hard carbon prepared using different biomass precursors in Examples 1, 2, and 3 of the present invention.

[0020] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0021] To avoid redundancy, the items used in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0022] Example 1 A preparation process for converting waste biomass into pulse hard carbon at high value based on transient high temperature, comprising the following steps: Under argon atmosphere, separate cotton was placed in a tubular furnace and carbonized at 800℃ for 1.5h, then placed in a vacuum oven at 80℃ and dried for 12h, cooled to room temperature and ground evenly to obtain biochar; then, the biochar was placed on the top of the carbon cloth, the positive and negative wires were connected to the two ends of the carbon cloth, the constant current power supply parameters were set to 50A, and the carbon cloth temperature was detected in real time by a thermal radiation thermometer, so that the temperature of the cotton-based biochar rose to 1800℃ within 100ms, then kept warm for 20s, repeated once, and finally cooled naturally, cooling to 500℃ within 1 second to obtain pulse hard carbon.

[0023] Example 2 A preparation process for converting waste biomass into pulsed hard carbon based on transient high temperature is similar to Example 1, except that the biomass precursor is a single peanut shell.

[0024] Example 3 A preparation process for realizing high-value conversion of waste biomass into pulse hard carbon based on transient high temperature, similar to example 1, the difference is that the biomass precursor is glucose.

[0025] The biochar, pulse hard carbon, acetylene black and PVDF obtained in example 1, example 2, example 3 are mixed in a mass ratio of 80:10:10, then homogenized to prepare a negative electrode material, and a negative electrode sheet is prepared on a 6um thick Cu foil, and a sodium sheet is used as a counter electrode, and an electrolyte is 1.0 M NaPF6 dissolved in a mixed solution of EC:DMC (volume ratio of 1:1), and a button cell is prepared in a glove box. Then test the discharge capacity of the above button cell at a current density of 0.2C, the voltage range is 2V~0.004V, the results are shown in Table 1: Table 1 As shown in the above Table 1, the capacity of the hard carbon negative electrode obtained by optimizing the three kinds of biomass precursors through transient high temperature is greatly improved, which proves the effectiveness of the technology in the preparation of biomass hard carbon, and provides an important technical approach for the high-value utilization of waste biomass.

[0026] Comparative example 1 The preparation process of traditional hard carbon includes the following steps: Under an argon atmosphere, the cotton is carbonized in a tube furnace at 800℃ for 1.5h, then dried in a vacuum oven at 80℃ for 12h, cooled to room temperature and ground uniformly to obtain cotton-based biochar, then heated from room temperature to 1500℃ at a rate of 5℃ / min, and kept for 2h, then naturally cooled to room temperature to obtain traditional hard carbon.

[0027] The crystal structure parameters of the biochar, pulse hard carbon and traditional hard carbon obtained in example 1 are shown in Table 2: Table 2 Crystal structure parameters of carbon materials From the experimental results in Table 2, it can be seen that the pulse hard carbon obtained by the present application benefits from the "freezing" effect of transient high temperature, so that the graphite microcrystals are in the right position, avoiding the abnormal growth of La caused by traditional long-time carbonization and the large decrease of d 002 .

[0028] The scanning electron microscope images of the biochar, pulse hard carbon obtained in example 1 and traditional hard carbon obtained in comparative example 1 are shown in Figure 1 From the figure, it can be seen that the pulse hard carbon changes into small size block due to the "explosive" heating rate in the preparation process, while the hard carbon obtained by the traditional method still maintains the original pore structure, which is not conducive to the short-range diffusion of electrons and ions.

[0029] The high-resolution transmission electron microscope images of the biochar, the pulse hard carbon obtained in the embodiment 1 of the present application and the traditional hard carbon obtained in the comparative example 1 are shown in the following figure Figure 2 As can be seen from the figure, the pulse hard carbon has abundant pore structure and can perfectly avoid the generation of graphitization, compared with the traditional hard carbon, although the crystallinity of the pulse hard carbon is poor, and the edge graphitization of the traditional hard carbon is serious, which will seriously hinder the embedding and pore filling of sodium ions.

[0030] The Raman spectra of the biochar, the pulse hard carbon obtained in the embodiment 1 of the present application and the traditional hard carbon obtained in the comparative example 1 are shown in the following figure Figure 3 As can be seen from the figure, although the intensity of the pulse hard carbon at 1580cm -1 is relatively low compared with the traditional hard carbon, the half-peak width is significantly reduced, and the 2D peak at 2650cm -1 is obviously increased, which indicates that the structure of the pulse hard carbon in the short-range microstructure is more ordered.

[0031] As Figure 4 : the electrochemical performance and cost comparison of the pulse hard carbon prepared in the present application and the traditional hard carbon prepared by the traditional carbonization method and the biochar; it can be seen that the pulse hard carbon can ensure low cost while obtaining higher capacity The charge-discharge curves (first week) of the biochar, the pulse hard carbon obtained in the embodiment 1 of the present application and the traditional hard carbon obtained in the comparative example 1 are shown in the following figure Figure 5 As can be seen from the figure, the pulse hard carbon prepared in the embodiment 1 of the present application is superior to the traditional hard carbon and the biochar in terms of both the first coulombic efficiency and the discharge capacity.

[0032] The X-ray diffraction patterns of the biochar, the pulse hard carbon obtained in the embodiment 1 of the present application and the traditional hard carbon obtained in the comparative example 1 are shown in the following figure, which further illustrates the "freezing effect" of the transient high temperature in the present application. Figure 6

[0033] The performance optimization results of the pulse hard carbon prepared by using different biomass precursors in the embodiment 1, the embodiment 2 and the embodiment 3 of the present application are shown in the following figure, which illustrates that the performance of the pulse hard carbon obtained by using various biomass precursors through the preparation process of the present application can be well improved. Figure 7

[0034] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the patent protection scope of the present application.​​

Claims

1. A preparation process for converting waste biomass into high-value pulse hard carbon based on transient high temperature, characterized in that: The method comprises the following steps: firstly, pre-carbonizing the biomass precursor under an inert atmosphere, and then naturally cooling it to room temperature to form biochar; then, loading the biochar on carbon cloth, and using a transient high-temperature heating method to rapidly heat and cool the carbon cloth to obtain pulse hard carbon.

2. The preparation process according to claim 1, wherein: The biomass precursor is at least one of cotton, peanut shells, and glucose.

3. The preparation process according to claim 1, wherein: The inert atmosphere is at least one of argon, helium, and nitrogen.

4. The preparation process according to claim 1, wherein: The pre-carbonization treatment temperature is 600-900°C.

5. The preparation process according to claim 1, wherein: The transient high-temperature heating temperature is 1000-2000° C., and the heating time is 10-60 seconds.

6. The preparation process according to claim 1, wherein: The rapid heating rate is 10 2 -10 5 ℃ / s.

7. The preparation process according to claim 1, characterized in that: The rapid cooling rate is 10-10 3 ℃ / s.

8. The preparation process according to claim 1, wherein: The rapid cooling method is at least one of natural cooling, air cooling, and water cooling.

9. A pulse hard carbon, characterized in that: The invention is prepared by the preparation process according to any one of claims 1 to 8.

10. Use of the pulse hard carbon according to claim 9 in preparing sodium ion battery or lithium ion battery materials.

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