Sodium ion battery hard carbon negative electrode material and preparation method thereof

Abstract

The present application relates to a kind of sodium ion battery negative material and its preparation method, the sodium ion battery negative material is the surface of lignin-based carbon coated in phenolic resin-based carbon of three-dimensional net structure, the sodium ion battery negative material is obtained by high-temperature carbonization with phenolic resin and ozone-activated alkaline lignin as carbon source, the ozone-activated alkaline lignin is obtained by activating alkaline lignin in ozone atmosphere at room temperature.The present application selects ozone-activated alkaline lignin as crosslinking agent, which can form C=O sodium storage active functional group with phenolic resin, and can be uniformly coated on the surface of phenolic resin sphere during pre-oxidation process, to build three-dimensional conductive network.The synergistic effect of the two can improve the transmission rate of sodium ion in the process of charge and discharge, and improve the reversible capacity and rate performance of the material.The raw materials selected by the present application are all industrial-grade raw materials, with the characteristics of low cost and abundant source, and good industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a hard carbon anode material for sodium-ion batteries and its preparation method. Background Technology

[0002] With technological advancements and population growth, the demand for environmentally friendly new energy sources is increasing. In response, researchers have proposed various new energy sources in recent years. Lithium-ion batteries, with their excellent electrochemical performance, have become the most widely used rechargeable battery. However, the scarcity and uneven distribution of lithium in nature significantly limits the further large-scale application of lithium-ion batteries. In the era of "beyond lithium-ion batteries," rechargeable sodium-ion batteries, with their advantages of low cost, high sodium abundance, and wide distribution of sodium resources, have become an important energy storage technology. They are widely used in renewable energy integration, electric vehicles, and energy storage systems. The negative electrode material, as a key component of sodium-ion batteries, plays a crucial role in their development. However, sodium... + radius Compared to Li + radius Larger and Na + The thermodynamic instability of graphite anodes has hindered the development and application of sodium-ion batteries. This limitation has spurred considerable efforts to develop a wide range of advanced sodium-ion battery anode materials.

[0003] Hard carbon anode materials have attracted widespread attention from researchers due to their advantages such as wide availability of precursors, simple preparation process, environmental friendliness, high safety, and low cost. The main factors affecting the electrochemical performance of hard carbon anode materials include graphite interlayer spacing, pore structure, heteroatom doping, and defects. Among these, pore structure and heteroatom doping have a more significant impact on the electrochemical performance of hard carbon anode materials. Creating a certain number of pores in the material can improve the reversible capacity and accelerate Na+ regeneration. + The adsorption and desorption rates of Na can be increased, thereby improving the rate performance of the material. Introducing suitable heteroatoms can also accelerate the adsorption and desorption of Na. + The adsorption process enhances the rate performance and reversible capacity of the material.

[0004] Traditional phenolic resin hard carbon anode materials suffer from several scientific problems, including insufficient conductivity and poor rate performance. Therefore, it is necessary to develop an improved method for preparing hard carbon anode materials to overcome these problems and improve the performance and energy density of sodium-ion batteries. Huang Yujie et al. used polyimide as a precursor and rationally designed carbon nanodots to obtain a hard carbon anode material with a rich pore structure. This material exhibits high conductivity at 0.1 Ag⁻¹. -1 It has 220 mAh g at current density -1Advanced Functional Materials.2023,2308392). Zheng et al. synthesized hard carbon materials with a large number of pore structures by CO2 etching method using starch as carbon source. The material has a reversible specific capacity of 320 mAh g-1 at 0.2 Ag-1, and a capacity of 171 mAh g-1 at 0.8 Ag-1(Advanced Energy Materials.2023,2303064). Wu et al. obtained boron-doped hard carbon materials using boric acid and glucose as boron and carbon sources, respectively. The material has a capacity of 80 mAh g-1 at 1 Ag-1(Journal of Materials Chemistry A.2022,10,17225). However, the capacity of the above-mentioned materials at 2 Ag-1 is below 100 mAh g-1, and the poor rate performance cannot meet the commercial needs of batteries. -1 -1 -1 -1 -1 -1 -1 -1

[0005] There are many reports in the prior art of using phenolic resin and lignin as carbon source to prepare hard carbon materials. For example, CN117326546A, CN116395668A, CN116969441A, CN114044508A, and CN108217623A. However, lignin only plays the role of carbon source, and cannot fully exert the characteristics of lignin that can easily form highly reactive hydroxyl radicals, resulting in the need to improve the electrochemical performance of the obtained hard carbon materials. SUMMARY

[0006] In order to solve the defects in the prior art that the hard carbon materials prepared based on phenolic resin and lignin have poor rate performance, and the capacity and cycle stability cannot meet the requirements at a large current density, the present application proposes an improved strategy of using ozone-activated alkaline lignin and constructing it on the surface of phenolic resin spheres to form a three-dimensional conductive network. The present application provides the following technical solutions to solve the above technical problems:

[0007] A sodium ion battery negative material is a three-dimensional network structure of lignin-based carbon coated on the surface of phenolic resin-based carbon. The sodium ion battery negative material is obtained by high-temperature carbonization of phenolic resin and ozone-activated alkaline lignin as carbon source. The ozone-activated alkaline lignin is obtained by activating alkaline lignin in an ozone atmosphere at room temperature.

[0008] ​​​​​​​​Further, the alkaline lignin is placed in an ozone atmosphere for 3-10 h, preferably 4-6 h.

[0009] Further, the ozone-activated alkaline lignin accounts for 30-50% of the total mass of the ozone-activated alkaline lignin and the phenolic resin.

[0010] The application also provides a preparation method of the sodium ion battery negative electrode material.

[0011] (S1) placing alkaline lignin in a reactor, connecting the reactor to an ozone generator, and introducing ozone gas into the reactor to ozone-activate the alkaline lignin at room temperature;

[0012] (S2) uniformly mixing the phenolic resin and the ozone-activated alkaline lignin and placing them in a muffle furnace for pre-oxidation;

[0013] (S3) placing the pre-oxidized mixture in a tube furnace for low-temperature pre-carbonization and high-temperature carbonization in an inert gas atmosphere to obtain the desired sodium ion battery hard carbon negative electrode material.

[0014] The preparation of the phenolic resin is well known in the art and is obtained by polymerization of diphenol compounds and formaldehyde, such as in a specific embodiment of the application, resorcinol is placed in an alcohol aqueous solution and ultrasonically dissolved, deionized water and ammonia water are added to the obtained solution under stirring, formaldehyde is then added, and after continuous stirring, centrifugation and drying, the phenolic resin is obtained.

[0015] Further, the volume-to-mass ratio of the formaldehyde solution and the resorcinol is (1-2) mL:1 g; the formaldehyde is added in the form of a formaldehyde aqueous solution, and the mass concentration of the formaldehyde is 30-40 wt%; and the concentration of the ammonia water solution is 20-30%.

[0016] Further, in step (S1), the ratio of the flow rate of ozone to the mass of alkaline lignin is 0.3-0.5 L / min / kg, and the ozone activation time should be controlled within 3-10 h, preferably 4-6 h. By adjusting the ozone activation time, the degree of ozonation of the alkaline lignin can be controlled. If the degree of ozonation is too high, the alkaline lignin will be excessively oxidized, which will in turn lead to a decrease in the crosslinking activity of the alkaline lignin. If the degree of ozonation is too low, the oxidation degree will not be sufficient, and sufficient active reaction functional groups cannot be generated, which is not conducive to the crosslinking reaction between the lignin and the phenolic resin.

[0017] Further, in step (S2), the ozone-activated alkaline lignin accounts for 30-50% of the total mass of the ozone-activated alkaline lignin and the phenolic resin, and the uniform mixing method is ball milling or a high-speed mixer.

[0018] Further, in step (S2), the pre-oxidation temperature should be controlled within 200-300℃, and the pre-oxidation time is 3-5 h.

[0019] Further, in step (S3), the inert atmosphere is nitrogen and / or argon, the heating rate is 1-5 DEG C / min, the low-temperature pre-carbonization is treated at 350 DEG C-500 DEG C for 1-3h, and the high-temperature carbonization is treated at 1200-1500 DEG C for 2-5h. The low-temperature residence carbonization can effectively promote the escape of small molecules in the material, form sufficient pore structures in the interior and surface of the material, and be beneficial to the storage and transportation of sodium ions.

[0020] The present application has the following beneficial technical effects:

[0021] The present application selects the ozone activation modified lignin strategy to introduce high-reactivity hydroxyl radicals into lignin, and makes cross-linking reaction with phenolic hydroxyl groups on the phenolic resin, forms C=O sodium storage active sites, and uniformly constructs a three-dimensional conductive network on the surface of the phenolic sphere, so that the hard carbon material has excellent reversible capacity and rate, further improves the electrochemical performance of the sodium ion battery, and is expected to promote the development and application of the sodium ion battery.

[0022] The sodium ion battery hard carbon negative electrode material synthesized by the present application has low price of raw materials and is environment-friendly. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The scanning electron microscope graph of the sodium ion battery hard carbon negative electrode material in Example 1.

[0024] Figure 2 The transmission electron microscope graph of the porous hollow carbon sphere negative electrode material particle prepared in Example 1.

[0025] Figure 3 The high-resolution transmission electron microscope graph of the porous hollow carbon sphere negative electrode material particle prepared in Example 1.

[0026] Figure 4 The scanning electron microscope graph of the sodium ion battery hard carbon negative electrode material in Comparative Example 1.

[0027] Figure 5 The charge-discharge curve graph of the sodium ion battery hard carbon negative electrode material in Example 1 when used.

[0028] Figure 6 The battery capacity retention performance graph under different current densities in Example 1. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. The following examples facilitate better understanding of the present application, but do not limit the present application. In the following examples, the experimental methods are conventional methods, unless otherwise specified.

[0030] Example 1

[0031] (1) Preparation of negative electrode material

[0032] 3 kg of resorcinol was dissolved in 100 L of a 9:1 mixture of ethanol and water, and was stirred at a stirring speed of 400 rpm by a magnetic stirrer. Then, 18 L of ammonia water (29 wt%) and 4 L of formaldehyde (40 wt%) were slowly added to the above solution in sequence to induce a polymerization reaction. After the above mixture was continuously stirred for 24 h, the obtained phenolic resin microspheres were centrifuged, washed with deionized water and ethanol, and then dried. The alkaline lignin was placed in a reactor, the reactor was connected to an ozone generator, and the ratio of ozone flow rate to alkaline lignin mass was adjusted to 0.3 L / min / kg. The alkaline lignin was activated in an ozone atmosphere for 4 h, and then removed. The phenolic resin and the ozone-activated alkaline lignin were thoroughly mixed by hand grinding for 20 min at a mass ratio of 7:3, and then the mixture was placed in a muffle furnace and pre-oxidized at 300℃ at a heating rate of 2℃ / min for 5 h to obtain an intermediate. Subsequently, the obtained intermediate was heated to 450℃ at a heating rate of 2℃ / min under an Ar atmosphere, and then held for 2 h. Thereafter, the temperature was continuously increased to 1400℃, and the carbonization was performed for 3 h to obtain the desired hard carbon material.

[0033] (2) Preparation of negative electrode sheet

[0034] The negative electrode material obtained in step (1), the conductive additive Super P, and the binder PVDF were mixed at a weight ratio of 90 parts, 5 parts, and 5 parts, respectively, and dissolved in a solvent NMP to obtain a uniform slurry. Then, the slurry was uniformly coated on a carbon-coated copper foil by using a 75 μm doctor blade, dried, and sliced to obtain a negative electrode sheet.

[0035] (3) Assembly of sodium ion battery

[0036] The prepared negative electrode sheet was assembled with a metal sodium negative electrode to obtain a sodium ion battery. The electrolyte was 1 M sodium hexafluorophosphate (NaPF6) dissolved in diethylene glycol dimethyl ether (DEGDME), and the separator was a porous glass fiber separator (whatman, GF / D). The button cell was assembled in an argon glove box with a water and oxygen value of less than 0.1 ppm, and electrochemical tests were performed. The electrochemical performance tests were performed on a N EWARE BTS-4000 battery test system at room temperature of 25℃.

[0037] Example 3

[0038] The other conditions are the same as in Example 1, except that the mass ratio of phenolic resin to ozone-activated alkaline lignin in step (1) is 1:1.

[0039] Example 4

[0040] The other conditions are the same as in Example 1, except that the mass ratio of phenolic resin to ozone-activated alkaline lignin in step (1) is 7:3.

[0041] Example 5

[0042] The other conditions are the same as in Example 1, except that the mass ratio of phenolic resin to ozone-activated alkaline lignin in step (1) is 2:8.

[0043] Example 6

[0044] The other conditions are the same as in Example 1, except that the alkaline lignin is placed in an ozone atmosphere for 6 hours in step (1).

[0045] Example 7

[0046] The other conditions are the same as in Example 1, except that the alkaline lignin is placed in an ozone atmosphere for 3 hours in step (1).

[0047] Example 8

[0048] The other conditions are the same as in Example 1, except that the alkaline lignin in step (1) is placed in an ozone atmosphere for 10 hours.

[0049] Comparative Example 1

[0050] The other conditions are the same as in Example 1, except that in step (1), alkaline lignin is replaced with crystalline cellulose.

[0051] Comparative Example 2

[0052] The other conditions are the same as in Example 1, except that in step (1), alkaline lignin is replaced with hemicellulose.

[0053] Comparative Example 3

[0054] The other conditions are the same as in Example 1, except that in step (1), ozone-activated alkaline lignin is replaced with an equal mass of alkaline lignin, that is, the alkaline lignin is not ozone-activated.

[0055] Application examples Testing of electrochemical performance

[0056] The sodium-ion batteries prepared in the above examples and comparative examples were subjected to rate performance tests: the test voltage was between 0.001-3V, and the tests were conducted at 0.05, 0.1, 0.5, and 1Ag. -1The specific capacity of the sodium ion battery prepared by the method of the present application is shown in Table 1 below.

[0057] Table 1: Rate performance data of sodium ion battery

[0058]

[0059]

[0060] It can be seen from the above results that the sodium ion battery hard carbon negative electrode material prepared by the present application has good electrochemical performance, excellent rate performance and cycle stability, which shows that the selection of self-synthesized phenolic resin and ozone-activated alkaline lignin for mixing and pre-oxidation is successful. The hard carbon negative electrode material prepared by the present application is a solid spherical material with a diameter of about 1 μm, which is not easy to be damaged in the cycle process, thereby having good cycle stability. The ozone-activated alkaline lignin is selected as a crosslinking agent in the pre-oxidation process, and the phenolic resin and the ozone-activated alkaline lignin not only produce crosslinking to obtain more C=O sodium storage active functional groups, but also coat a layer of three-dimensional conductive network, so that the material can improve the sodium ion diffusion rate and promote the electron transmission without losing the capacity of the material, thereby having good rate performance and capacity retention rate. At a current density of 1 Ag -1 , the capacity is still as high as 312 mAh g -1 , and the capacity retention rate is 92.6% after 200 cycles.

[0061] Figure 1 Figure 1 is a scanning electron microscope image of the sodium ion battery hard carbon negative electrode material obtained in Example 1, from which it can be seen that the synthesized negative electrode material is successfully coated with a three-dimensional conductive network. The coating of the network is formed by crosslinking reaction of the hydroxyl groups in the phenolic resin and the hydroxyl radicals in the activated lignin. In the pre-oxidation process, small molecular substances are overflowed due to the crosslinking reaction, thereby forming a large number of pore structures, which are beneficial to the diffusion of sodium ions in the battery charging and discharging process, and can greatly improve the rate performance of the sodium ion battery. In addition, the structure of the solid hard carbon sphere is relatively stable, so that the material has good structural stability in the cycle process, thereby improving the cycle performance of the sodium ion battery.

[0062] Figure 2 Figure 2 is a transmission electron microscope image of the sodium ion battery hard carbon negative electrode material obtained in Example 1, from which it can be seen that the synthesized negative electrode material has a uniformly coated three-dimensional conductive network, which has the same micro-morphology as observed in the scanning image. The coated layer with high conductivity can promote the rapid transmission kinetics of sodium ions, thereby promoting the rate performance of the material; and the more C=O functional groups can effectively increase the reversible capacity of the material.

[0063] Figure 3 is a high-resolution transmission electron microscope image of the obtained sodium ion battery hard carbon negative electrode material. As can be seen from the figure, the graphitization degree of the surface of the synthesized negative electrode material is high, and the lattice fringes are ordered. The high graphitization degree of the surface layer of the material can provide a fast transmission channel for sodium ions during charging and discharging, thereby improving the sodium ion transmission rate and further improving the rate performance of the material.

[0064] Figure 4 is a scanning electron microscope image of the electrode material (Comparative Example 1) obtained by mixing the ozone-activated alkaline lignin with phenolic resin without pre-oxidation and high-temperature calcination. As can be seen from the figure, the alkaline lignin without ozone activation cannot be complexed with phenolic resin to form a coating layer. This is because ozone activation can introduce highly reactive hydroxyl radicals into the lignin, and cross-linking reactions occur with the phenolic hydroxyl groups on the phenolic resin, forming C=O sodium storage active sites and uniformly constructing a three-dimensional conductive network on the surface of the phenolic sphere. The alkaline lignin without ozone activation cannot form highly reactive hydroxyl radicals, so it cannot cross-link with the phenolic resin.

[0065] Figure 5 is a charging and discharging curve diagram of the sodium ion battery hard carbon negative electrode material in Example 1 when in use. Figure 6 Testing of electrochemical performance is a battery capacity retention performance diagram under different current densities in Example 1.

Claims

1. A sodium-ion battery anode material, characterized in that, The lignin-based carbon with three-dimensional network structure is coated on the surface of the phenolic resin-based carbon, and the sodium ion battery negative electrode material is obtained by high-temperature carbonization of phenolic resin and ozone-activated alkaline lignin as carbon sources.

2. The sodium-ion battery anode material of claim 1, wherein, The alkaline lignin is activated in the ozone atmosphere for 3-10 hours.

3. The sodium-ion battery anode material of claim 2, wherein, The alkaline lignin is activated in the ozone atmosphere for 4-6 hours.

4. The sodium-ion battery anode material of claim 1, wherein, The ozone-activated alkaline lignin accounts for 30-50% of the total mass of the ozone-activated alkaline lignin and the phenolic resin.

5. The method for preparing the sodium-ion battery anode material according to any one of claims 1-4, characterized in that, The method comprises the following steps: (S1) placing alkaline lignin in a reactor, connecting the reactor to an ozone generator, and introducing ozone gas into the reactor to activate the alkaline lignin in an ozone atmosphere at room temperature; (S2) uniformly mixing phenolic resin and ozone-activated alkaline lignin and placing them in a muffle furnace for pre-oxidation; (S3) placing the pre-oxidized mixture in a tube furnace for low-temperature pre-carbonization and high-temperature carbonization in an inert gas atmosphere to obtain the desired sodium ion battery hard carbon negative electrode material.

6. The production method according to claim 5, wherein In step (S1), the ratio of the flow rate of ozone to the mass of alkaline lignin is 0.3-0.5 L / min / kg, and the ozone activation time should be controlled within 3-10 hours.

7. The production method according to claim 6, wherein In step (S1), the ozone activation time should be controlled within 4-6 hours.

8. The preparation method according to claim 5, characterized in that, In step (S2), the ozone-activated alkaline lignin accounts for 30-50% of the total mass of the ozone-activated alkaline lignin and the phenolic resin.

9. The preparation method according to claim 5, characterized in that, In step (S2), the pre-oxidation temperature should be controlled within 200-300℃, and the pre-oxidation time is 3-5 hours.

10. The method of claim 5, wherein, In step (S3), the inert atmosphere is nitrogen and / or argon, the heating rate is 1-5℃ / min, the low-temperature pre-carbonization is treated at 350℃-500℃ for 1-3 hours, and the high-temperature carbonization is treated at 1200-1500℃ for 2-5 hours.

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