Preparation method for using lotus petiole derived hard carbon as negative electrode of sodium ion battery

Abstract

The invention belongs to the field of sodium-ion batteries, and particularly relates to a preparation method of lotus petiole derived hard carbon as a negative electrode of a sodium-ion battery. Firstly, lotus petiole is subjected to pretreatment such as washing and drying to remove surface impurities, then a pretreated material is obtained by adopting a microwave-assisted and chemical treatment method, and finally, the hard carbon material with good stability is obtained by high-temperature carbonization in a nitrogen atmosphere. The half-cell assembled by the biomass derived hard carbon prepared by the invention has excellent electrochemical performance. In the preparation process, raw materials are cheap and easy to obtain, the cost is low, the method is simple and easy to implement, the preparation efficiency is high, and no template or surfactant exists. A half battery assembled by the prepared hard carbon material has relatively high specific capacity, has the reversible capacity of 342.4 mAh g <-1 > under the current density of 20 mA g <-1 >, and still has the capacity retention rate of 90.2% after 2000 cycles under the current density of 1 A g <-1 >. In addition, the natural lotus petiole is used as the raw material, the material is easy to obtain and low in cost, and comprehensive utilization of biomass waste is achieved.

Description

Technical Field

[0001] The invention belongs to the field of sodium ion secondary batteries, and in particular relates to a method for preparing a sodium ion battery negative electrode using a lotus stem-derived hard carbon. Technical Background

[0002] Sodium-ion batteries have excellent low-temperature performance and safety, making them the next generation of energy storage batteries with the greatest development potential. Under current conditions, due to the relative scarcity of lithium resources, developing a new generation of energy storage batteries has become an important strategy. Sodium has become the most promising new secondary battery energy storage technology for large-scale energy storage systems due to its high abundance, wide global distribution, low price, and similar physical and chemical properties to lithium. However, compared with lithium ions, sodium ions cannot form a stable thermodynamic structure in graphite due to their larger ionic radius, and cannot use graphite as the negative electrode like lithium ions, so a larger interlayer spacing is required to allow sodium ions to be reversibly stored. Hard carbon, as a carbon material that is difficult to graphitize, has a large interlayer spacing of more than 0.37nm, making it the most ideal material for the negative electrode of sodium ion batteries.

[0003] The biomass hard carbon materials reported so far generally include coconut shells, starch, straw powder, resin-based materials, etc., but these biomass-derived hard carbons all show low coulombic efficiency, poor cycle stability and rate performance. Among them, the resin-based materials are limited in their development due to their relatively expensive prices and certain pollution to the environment. In addition, the conventional processing methods have complex processing processes, which also increase their preparation costs. In this paper, a microwave-assisted combined with chemical treatment method is used to pretreat the precursor material efficiently and quickly, and other contents such as cellulose, hemicellulose, lignin and ash in biomass can be controlled and adjusted, which greatly reduces the preparation time and cost and improves the consistency of materials; in addition, the wide distribution of lotus stems, easy collection, and waste utilization also make it have development potential. Therefore, the use of microwave-assisted combined with chemical treatment methods to pretreat lotus stem powder to prepare sodium ion battery hard carbon negative electrode materials solves the problems of high prices and environmental pollution in traditional carbon material preparation methods, which has great research significance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing lotus stem-derived hard carbon for use as a negative electrode for sodium ion batteries in view of the above-mentioned deficiencies in the existing technology. A rapid physical and chemical method is used to modify biomass materials to obtain a negative electrode material for sodium ion batteries with good electrochemical properties. The prepared hard carbon material sodium ion battery negative electrode has a higher specific capacity and better rate performance.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: The method for preparing hard carbon derived from lotus stems as a negative electrode for sodium ion batteries comprises the following steps: firstly, pretreating lotus stems to remove surface impurities; then, carbonizing by microwave-assisted and chemical treatment in one step to obtain a negative electrode material of biomass-derived hard carbon with good electrochemical performance, comprising the following steps: S1: Place the precursor material in a microwave reactor, add sulfuric acid solution, react for a period of time, and then filter and wash.

[0006] S2: The processed material is pyrolyzed at high temperature in a protective atmosphere using a graphite crucible as a carrier to prepare a biomass-derived hard carbon negative electrode material with regulated composition.

[0007] Further, the sulfuric acid solution is prepared by the following steps: Add some deionized water to a volumetric flask, add 98% concentrated sulfuric acid to the volumetric flask, dilute to obtain a sulfuric acid solution with a concentration of 0.5-1.5 mol / L, and cool to room temperature before use.

[0008] Preferably, the concentration of the sulfuric acid solution is 1 mol / L.

[0009] Further, the precursor is subjected to microwave reaction time, using the following steps: The carbon source precursor was reacted in a microwave reactor for 0 min, 5 min, 10 min and 20 min respectively.

[0010] Preferably, the reaction time is 10 min.

[0011] Further, the precursor is subjected to microwave-assisted reaction temperature, using the following steps: The carbon source precursor was reacted in a microwave reactor at 120° C., 160° C., and 200° C., respectively.

[0012] Preferably, the microwave reaction temperature is 160°C.

[0013] Preferably, the reaction carrier is a graphite crucible.

[0014] Preferably, the high temperature calcination conditions are: calcination temperature 1200°C-1400°C, calcination time 3h.

[0015] Furthermore, the obtained biomass-derived hard carbon material is mixed according to the above characteristics: the hard carbon, conductive carbon black (conductive agent) and sodium carboxymethyl cellulose (binder) are mixed at a mass ratio of 80:10:10, the obtained mixture is fully ground in a mortar, an appropriate amount of deionized water is added with a pipette, and the mixture is fully ground again to obtain a uniform slurry, which is coated on aluminum foil. After being placed in a vacuum drying oven at 90°C for 12 hours to completely evaporate the solvent, the pieces are cut, weighed, and the active material loading is calculated.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention provides a microwave-assisted one-step carbonization method combined with chemical treatment, which has a short reaction time and can obtain a hard carbon material derived from a lotus stem with good electrochemical properties. The present invention uses natural lotus stems as raw materials, which are easy to obtain, low in cost, simple and easy to operate, and does not require templates and surfactants, thereby realizing the comprehensive utilization of biomass waste. The sodium ion battery negative electrode material prepared by this method effectively reduces the specific surface area, increases the curvature of the carbon layer, increases the disorder of the material, forms more closed pore structures and reversible sites, and is conducive to the embedding and removal of sodium ions. The prepared hard carbon material sodium ion battery negative electrode has a high specific capacity, with a maximum specific capacity of 342.4 mAh g -1 After assembling it into a half-battery, after 2000 cycles, the average Coulombic efficiency was 99.89% and the capacity remained above 90%.

[0017] The above is an overview of the technical solution of the invention. The present invention will be further described below in conjunction with the accompanying drawings and specific implementation examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The hard carbon structure is regulated by different sulfuric acid concentrations as the negative electrode material of sodium ion batteries at 0-2.5V and 20 mAg -1 Charge and discharge curves at current density.

[0019] Figure 2 The hard carbon structure is regulated by different microwave reaction time as the negative electrode material of sodium ion battery at 0-2.5V and 20mA g -1 Charge and discharge curves at current density.

[0020] Figure 3 This is the TEM image of hard carbon structure regulated under optimal conditions by microwave-assisted combined with chemical treatment as a negative electrode material for sodium ion batteries.

[0021] Figure 4 It is the Raman diagram of the hard carbon structure as the negative electrode material of sodium ion battery controlled by microwave-assisted combined with chemical treatment with different microwave reaction times.

[0022] Figure 5 It is the XRD diagram of hard carbon structure as negative electrode material of sodium ion battery controlled by microwave-assisted combined with chemical treatment with different microwave reaction times.

[0023] Figure 6 The microwave reaction time under the best conditions is to combine microwave-assisted chemical treatment to regulate the hard carbon structure as anode material for sodium ion batteries at 0-2.5V and 1A g -1 Long cycle diagram under current density of .

[0024] Figure 7It is to implement the microwave reaction time under the best conditions and microwave-assisted combined with chemical treatment to regulate the hard carbon structure as the negative electrode material of sodium ion battery at 0-2.5V, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5mAh g -1 Rate diagram at current density of . DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0026] The microwave-assisted combined chemical treatment provided in this experiment is used to control the hard carbon structure to achieve the preparation and application of high-performance sodium ion battery energy storage materials, including the following steps: S1: Soak 2.5 g of carbon source precursor in 50 ml of 1 mol / L H2SO4 solution and place it in a microwave reactor for reaction for 10 min.

[0027] S2: The obtained material is carried in a graphite crucible and carbonized at 1300°C in a nitrogen (N2) atmosphere for 3 hours to obtain a hard carbon material regulated by microwave-assisted combined with chemical treatment.

[0028] S3: Grind the powder obtained by carbonization thoroughly, mix the hard carbon, conductive carbon black and sodium carboxymethyl cellulose in a mass ratio of 80:10:10, grind the mixture thoroughly in a mortar, add an appropriate amount of deionized water with a pipette, grind and mix thoroughly again to obtain a uniform slurry, and apply it on aluminum foil. Place it in a vacuum drying oven at 90°C for 12 hours to completely evaporate the solvent, and use a cutting machine (MSK-T10) to cut it into round-grade pieces with a diameter of 10 mm, weigh it, and calculate the mass of the active substance to be 0.8-0.9 mg.

[0029] Electrochemical performance test of the microwave-assisted combined with chemical treatment hard carbon material prepared in this example: Sodium metal was used as the counter electrode, the electrolyte was 1 mol / L NaPF6(DEGDME), and the separator was glass fiber (GF / C). C2032 button cells were assembled in a glove box filled with argon (Ar). The charge and discharge performance tests were conducted using the battery test system of Shenzhen Xinwei Electronics Co., Ltd.

[0030] Combined with Figure 1 It shows that among the different sulfuric acid concentrations in the examples, the sulfuric acid concentration of 1 mol / L has the most obvious effect on the change of hard carbon capacity.

[0031] Combined with Figure 2 It shows that among the hard carbon materials regulated by different microwave reaction time, the best effect is achieved under a treatment time of 10 minutes.

[0032] Combined with Figure 3-5 It shows that microwave-assisted combined with chemical treatment has significantly changed the interlayer spacing and disorder of hard carbon.

[0033] Combined with Figure 6 It shows that the hard carbon materials regulated by microwave assistance combined with chemical treatment have good cycle stability and high capacity retention rate.

[0034] Combined with Figure 7 This indicates that hard carbon materials regulated by microwave-assisted chemical treatment have good rate performance. The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for preparing hard carbon derived from lotus stems for use as a negative electrode for sodium ion batteries, characterized in that: First, the lotus stems are pretreated to remove surface impurities; then, a one-step carbonization method with microwave assistance and chemical treatment is used to obtain a biomass-derived hard carbon anode material with good electrochemical performance, including the following steps: (1) The pretreatment includes washing, drying and crushing. The lotus stem powder is ultrasonically washed with deionized water and anhydrous ethanol for 0.5 to 2 h respectively to remove impurities on the surface of the material. After the ultrasonic washing is completed, the lotus stem powder is placed in a forced air drying oven at 60°C to 80°C for 6 to 12 h. The dried lotus stem is placed in a crusher and crushed to obtain powder. (2) The powder crushed in step (1) is placed in a microwave reactor, H2SO4 solution is added, the powder is taken out of the microwave reactor, cooled to room temperature, filtered, washed and dried; the temperature is raised to 1300°C in a tube furnace, and the temperature is maintained at a constant temperature for 3 h in a protective gas atmosphere. After the tube furnace is cooled to room temperature, a stem-derived hard carbon with a reasonable graphitized structure is obtained.

2. The method for preparing the lotus stem-derived hard carbon as a negative electrode for a sodium ion battery according to claim 1, characterized in that: In step (2), the solid-liquid ratio of the crushed powder to the sulfuric acid solution is 1:20, the crushed powder is sieved with 30-50 mesh, and the concentration of the sulfuric acid solution is 0.2-1.5 mol / L.

3. The method for preparing the lotus stem-derived hard carbon as a negative electrode for a sodium ion battery according to claim 1, characterized in that: In step (2), the microwave reaction temperature is 120-200° C., and the reaction time is 0-20 min.

4. The method for preparing the lotus stem-derived hard carbon as a negative electrode for a sodium ion battery according to claim 1, characterized in that: In step (2), the protective gas is nitrogen.

5. The method for preparing the lotus stem-derived hard carbon as a negative electrode for a sodium ion battery according to claim 1, characterized in that: In step (2), the heating rate is 10°C / min below 1000°C and 5°C / min above 1000°C.

6. The method for preparing the lotus stem-derived hard carbon as a negative electrode for a sodium ion battery according to claim 1, characterized in that: In step (2), by controlling the composition of the stem carbon source, the stem-derived hard carbon material is obtained. The Bragg equation is used to calculate the 002 interlayer spacing to be 0.380-0.386 nm, which can provide reversible embedding and extraction of sodium ions. Raman testing is also used to obtain the I D / I G It is 1.80, which has a reasonable graphitized structure.

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