Modified screening type carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion battery preparation, in particular to a modified screening type carbon negative electrode material and a preparation method and application thereof.The modified carbon material is obtained by coating the surface of porous carbon powder with a modified material, and coating of the modified material is double-layer coating of a coating material and a phase change material; the phase change material is at least one of paraffin, n-hexadecane, n-octadecane, fatty acid, stearic acid, palmitic acid high-density polyethylene, polyethylene glycol, alcohols and lipids; the coating material is heated and carbonized to coat the surfaces of the porous carbon particles to form a compact carbon layer, and then the phase change material is used for secondary coating, so that the pore size of the surface of the porous carbon is adjusted, the specific surface area of the porous carbon is reduced, meanwhile, the coherence of internal pore channels of the porous carbon can be reserved, and a solid-phase diffusion channel of sodium ions cannot be damaged; and rapid diffusion and storage of sodium ions in pore channels are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery preparation, and in particular to a modified screening-type carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] With the growing need for renewable energy storage and the rapid development of the electric vehicle industry, new electrochemical energy storage technologies are expected to mitigate the volatility associated with renewable energy generation connected to the grid and reduce greenhouse gas emissions, thereby achieving a win-win situation for both economic and social development and ecological protection. Flexible, cost-effective, safe, efficient, and rechargeable electrochemical energy storage devices are becoming an important option for energy storage in smart grids. Electrochemical energy storage systems, exemplified by lithium-ion batteries, offer advantages such as high energy density and excellent cycle stability, meeting the lightweight and thin requirements of modern portable energy storage devices. However, in the field of large-scale energy storage, lithium-ion batteries are limited by the low availability and high cost of their raw material, lithium, making them difficult to use in large-scale energy storage and the growing electric vehicle market. Therefore, researchers have turned their attention to alkali metals, the main group elements of the lithium family. Among these, sodium and potassium, with their natural abundance, offer promising application prospects for energy storage devices based on these elements.

[0003] Alkali metal ion batteries have a similar structure and working mechanism, which is to use the movement of ions between the positive and negative electrodes to achieve charging and discharging. Sodium ion batteries are a "rocking chair" type of battery that has a similar working principle to lithium ion batteries. With similar battery composition, they can effectively utilize the mature lithium ion battery industry chain to achieve leapfrog development. Mainstream sodium ion battery negative electrode materials mainly include carbon-based materials, metal elements, metal oxides and metal sulfides. Among them, metal elements, oxides and alloy negative electrodes have higher specific capacities, but they will cause volume expansion during the charging and discharging process, resulting in unstable temperature inside the battery, posing a major safety problem and affecting cycle performance.

[0004] Carbon materials are currently the most promising negative electrode materials for alkali metal ion batteries due to their high safety and cycle stability. However, due to their uneven pore size distribution and irregular pore shape, sodium ions need to constantly change direction during transmission, which increases diffusion resistance and time, thereby affecting the transmission rate and efficiency of sodium ions. This directly leads to the low platform capacity, low first coulombic efficiency, and poor rate performance commonly found in carbon materials in sodium ion batteries. At the same time, volume expansion during the charge and discharge process causes unstable internal temperature of the battery, making the charge and discharge process less stable in long-term cycling conditions and having a low capacity retention rate, which seriously hinders the industrialization process of sodium ion batteries. In the face of such problems, most existing technologies use a single layer coating on the surface of the carbon material, but this only solves the problems of conductivity and volume expansion of the electrode material, and has limited effect on optimizing the sodium ion transmission path and improving the pore size distribution. As a result, the platform capacity, first coulombic efficiency, rate performance, and cycle stability in long-term cycling conditions have not been significantly improved. Summary of the Invention

[0005] Based on the above problems, the present invention provides a modified screening type carbon negative electrode material and its preparation method and application. The carbon material adopts a double-layer coating technology of coating material and phase change material. On the basis of the coating material, the transmission path of sodium ions is further optimized by phase change material, thereby reducing the diffusion resistance. While reducing the pore size on the surface of the porous carbon particles, it does not affect the coherent pore structure inside the porous carbon particles, thereby achieving higher platform capacity, first coulomb efficiency and rate performance.

[0006] A modified screening type carbon negative electrode material is obtained by coating the surface of porous carbon powder with a modified material, wherein the modified material coating is a double layer coating of a coating material and a phase change material; wherein the coating material is coated on the surface of the porous carbon powder, and the phase change material is coated on the surface of the coating material.

[0007] Furthermore, the phase change material is at least one of paraffin, n-hexadecane, n-octadecane, fatty acid, stearic acid, palmitic acid high-density polyethylene, polyethylene glycol, alcohols, and lipids.

[0008] Furthermore, the coating material is at least one of glucose-derived carbon, phenolic resin carbon, starch, cyclodextrin, piperazine pyrophosphate, and chitosan.

[0009] Furthermore, the particle size D50 of the modified carbon material is 1 to 20 μm, the average pore size is 0.1 to 5 nm, and the specific surface area is 4 to 100 m 2 / g.

[0010] The present invention also provides a method for preparing a modified screening type carbon negative electrode material, comprising the following steps:

[0011] Step 1: Grinding a porous carbon precursor to obtain a porous carbon powder having abundant nanopores inside;

[0012] Step 2: uniformly mixing the porous carbon powder obtained in step 1 with the coating material and then grinding the mixture, subjecting the mixture to a heating and carbonization process, and cooling the mixture to obtain a first coating layer material;

[0013] Step 3: uniformly mix the first coating layer material obtained in step 2 with the phase change material, grind the mixture, and allow to stand to obtain a modified carbon material.

[0014] Furthermore, the porous carbon precursor in step 1 is at least one of microporous activated carbon, hierarchical porous activated carbon, template porous carbon, and porous graphene.

[0015] Furthermore, the particle size D50 of the porous carbon powder in step 1 is 1 to 20 μm, preferably 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0016] Furthermore, the average pore size of the porous carbon powder in step 1 is 0.1 to 3 nm, preferably 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm or 3 nm.

[0017] Furthermore, the specific surface area of ​​the porous carbon powder in step 1 is 500 to 3000 m 2 / g, preferably 500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g、2500m 2 / g、2600m 2 / g、2700m 2 / g、2800m 2 / g、2900m 2 / g or 3000m 2 / g.

[0018] Furthermore, in step 2, the mass ratio of the porous carbon powder to the coating material is 1:(0.02-5), preferably 1:(1-5), and more preferably 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0019] Furthermore, in step 3, the mass ratio of the first coating layer material to the phase change material is 1:(0.02~10), preferably 1:(1~10), and more preferably 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5 or 1:10.

[0020] Furthermore, the heating rate of the heating carbonization process in step 2 is 0.1 to 20 ° C / min, preferably 0.1 ° C / min, 0.5 ° C / min, 1 ° C / min, 2 ° C / min, 3 ° C / min, 4 ° C / min, 5 ° C / min, 6 ° C / min, 7 ° C / min, 8 ° C / min, 9 ° C / min, 10 ° C / min, 11 ° C / min, 12 ° C / min, 13 ° C / min, 14 ° C / min, 15 ° C / min, 16 ° C / min, 17 ° C / min, 18 ° C / min, 19 ° C / min or 20 ° C / min.

[0021] Furthermore, the heating temperature of the heating carbonization process in step 2 is 300-800°C, preferably 300°C, 320°C, 350°C, 370°C, 400°C, 420°C, 450°C, 470°C, 500°C, 520°C, 550°C, 570°C, 600°C, 620°C, 650°C, 670°C, 700°C, 720°C, 750°C or 800°C.

[0022] Furthermore, the holding time of the heating carbonization process in step 2 is 0.1 to 10 hours, preferably 0.1 hour, 0.3 hour, 0.5 hour, 0.7 hour, 1 hour, 1.2 hour, 1.5 hour, 2 hour, 2.5 hour, 3 hour, 3.5 hour, 4 hour, 4.5 hour, 5 hour, 6 hour, 7 hour, 8 hour, 9 hour or 10 hour.

[0023] Furthermore, the heating carbonization process in step 2 is carried out in a protective atmosphere, and the protective atmosphere is at least one of argon, nitrogen, ammonia and hydrogen.

[0024] Furthermore, the flow rate of the protective atmosphere in the heating carbonization process in step 2 is 10 to 100 mL / min, preferably 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, 60 mL / min, 64 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, 80 mL / min, 85 mL / min, 90 mL / min, 95 mL / min or 100 mL / min.

[0025] Furthermore, the cooling rate in step 2 is 0.1 to 20°C / min, preferably 0.1°C / min, 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min or 20°C / min.

[0026] Furthermore, the terminal temperature of cooling in step 2 is 10-40°C, preferably 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C.

[0027] Furthermore, the temperature of the standing process in step 3 is 50-80° C., and the standing time is 6-12 hours.

[0028] The carbon material prepared based on the above preparation method, which is coated with a coating material for a primary coating and a phase change material for a secondary coating, can be used as a negative electrode material in sodium ion batteries.

[0029] Furthermore, the positive electrode of the sodium ion battery is at least one of a transition metal layered oxide, a sodium polyanion compound, Prussian blue and Prussian white.

[0030] Furthermore, the electrolyte of the sodium ion battery includes an organic solvent and a sodium salt, the organic solvent is at least one of EC, PC, DMC, DEC, EMC, EA, FEC and VC, and the sodium salt is preferably at least one of NaClO4, NaPF6, NaBF4, NaFSI and NaTFSI.

[0031] Furthermore, the conductive agent in the sodium ion battery is at least one of SUPER-P, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF, acetylene black and Ketjen black.

[0032] Furthermore, the adhesive in the sodium ion battery is at least one of PVDF, CMC, SBR, PTFE, SA, PAA and PAN.

[0033] The advantages of the present invention are:

[0034] 1. The present invention adopts a double-layer coating technology of coating material and phase change material. By heating and carbonizing the coating material, a dense carbon layer is formed on the surface of the porous carbon particles. The dense layer can adjust the pore size of the porous carbon surface, reduce the specific surface area of ​​the porous carbon, and increase the sodium storage site; the phase change material is then used for secondary coating. The phase change material can provide a stable structural support for the carbon material and can also inhibit the volume expansion of the carbon material during the charge and discharge process, maintaining a relatively stable temperature environment. On the basis of the coating material, the phase change material is further used to optimize the transmission path of sodium ions, reduce the diffusion resistance, facilitate the directional movement of sodium ions in the pores, and will not affect the coherence of the internal pores of the porous carbon, will not destroy the solid-phase diffusion channel of sodium ions, and facilitate the rapid diffusion and storage of sodium ions inside the pores; the obtained double-layer coated carbon material can provide sufficient sodium storage space and realize rapid ion transmission at the same time, significantly improving the platform capacity, first coulomb efficiency and rate performance, and significantly improving the stability of the sodium ion battery in the long cycle state;

[0035] 2. The preparation method provided by the present invention simplifies the tedious and complicated preparation process in the prior art. It only requires one step of heating and carbonization and one step of static treatment to achieve two coatings. It is simple to operate and has low energy consumption. It has good application prospects in the field of sodium ion battery production and manufacturing.

[0036] 3. The coating material selected in the present invention has a suitable molecular dynamics diameter, which helps to adsorb on precisely matched porous carbon particles, thereby improving the quality and efficiency of the coating layer; the selected phase change material can absorb or release heat during the charging and discharging process, thereby stabilizing the temperature of the electrode material and reducing structural instability caused by temperature changes. While providing stable structural support for the carbon material, it can also further optimize the transmission path of sodium ions through its unique physical and chemical properties, reduce ion diffusion resistance, and provide a relatively stable temperature environment during the charging and discharging process, which is conducive to the directional movement of sodium ions in the pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a scanning electron microscope image of the carbon material in Example 1 of the present invention;

[0038] Figure 2 is a nitrogen adsorption and desorption curve of the carbon material in Example 1 of the present invention;

[0039] Figure 3 is a pore size distribution curve of the carbon material in Example 1 of the present invention;

[0040] Figure 4 This is a first cycle charge and discharge curve of the carbon material in Example 1 of the present invention;

[0041] Figure 5 is a scanning electron microscope image of the carbon material in Comparative Example 1 of the present invention;

[0042] Figure 6 is a nitrogen adsorption and desorption curve of the carbon material in Comparative Example 1 of the present invention;

[0043] Figure 7 is a pore size distribution curve of the carbon material in Comparative Example 1 of the present invention;

[0044] Figure 8 This is a first cycle charge and discharge curve of the carbon material in Comparative Example 1 of the present invention;

[0045] Figure 9 is a scanning electron microscope image of the carbon material in Comparative Example 2 of the present invention;

[0046] Figure 10 is a nitrogen adsorption and desorption curve of the carbon material in Comparative Example 2 of the present invention;

[0047] Figure 11 is a pore size distribution curve of the carbon material in Comparative Example 2 of the present invention;

[0048] Figure 12 This is a first cycle charge and discharge curve of the carbon material in Comparative Example 2 of the present invention;

[0049] Figure 13 is a scanning electron microscope image of the porous carbon powder in Comparative Example 3 of the present invention;

[0050] Figure 14 is a nitrogen adsorption-desorption curve of the porous carbon powder in Comparative Example 3 of the present invention;

[0051] Figure 15 is a pore size distribution curve of the porous carbon powder in Comparative Example 3 of the present invention;

[0052] Figure 16 This is a charge-discharge curve of the first cycle of the porous carbon powder in Comparative Example 3 of the present invention;

[0053] Figure 17 is a cyclic charge-discharge curve diagram of the carbon material in Example 1 of the present invention;

[0054] Figure 18 is the cyclic charge-discharge curve of the carbon material in Comparative Example 1 of the present invention;

[0055] Figure 19 is a cyclic charge and discharge curve diagram of the carbon material in Comparative Example 2 of the present invention;

[0056] Figure 20 3 is a cyclic charge-discharge curve of the porous carbon powder in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] It should be noted that the various installation methods and technical terms mentioned in the present invention are technical terms that have long been clearly known in the relevant technical field and therefore will not be further explained. In addition, the same reference numerals are used for the same components, but this does not affect nor constitute an accurate understanding of the technical solution by those skilled in the art.

[0059] Example 1

[0060] This embodiment provides a modified screening type carbon negative electrode material and a preparation method thereof. The modified carbon material is obtained by coating the surface of porous carbon powder with a double layer of coating material and phase change material, wherein the coating material is coated on the surface of the porous carbon powder, and the phase change material is coated on the surface of the coating material. The specific steps are as follows:

[0061] Step 1: Grind a porous carbon precursor (the porous carbon precursor in this embodiment is microporous activated carbon "activated petroleum coke AC-SYJ") to a particle size of about 10 μm to obtain a porous carbon powder with abundant nanopores inside;

[0062] Step 2: 0.5 g of the porous carbon powder obtained in step 1 was mixed evenly with 2.5 g of the coating material (the coating material in this embodiment is glucose-derived carbon), and then ground. The mixture was placed in a tube furnace, and a protective atmosphere with a flow rate of 64 mL / min (the protective atmosphere in this embodiment is argon) was introduced. The temperature was increased to 500 ° C at a heating rate of 5 ° C / min, and the reaction was carried out at a constant temperature of 500 ° C for 1 hour. After the reaction was completed, the mixture was cooled to room temperature (25 ° C) at a cooling rate of 5 ° C / min to obtain a first coating layer material.

[0063] Step 3: Take 0.5 g of the first coating layer material obtained in step 2 and 2.25 g of phase change material (the phase change material in this embodiment is paraffin), mix them evenly and grind them, heat them to 50°C and let them stand for 12 hours to allow them to fully react and wrap, and then cool them to room temperature to obtain the carbon material.

[0064] The carbon material obtained in this example is used as the negative electrode active material, Super-P is used as the conductive additive, and PVDF is used as the binder to assemble a sodium ion battery. The steps are as follows:

[0065] The negative electrode active material, conductive additive and adhesive are fully stirred and mixed in NMP in a mass ratio of 8:1:1 to form a negative electrode slurry, which is coated on a copper foil current collector and placed in a vacuum oven at 100°C for 12 hours to obtain a negative electrode sheet; the positive electrode active material is a transition metal layered oxide, and the positive electrode sheet is obtained by the same method; the electrolyte in the electrolyte is NaClO4, and the solvent is EC and DEC in a volume ratio of 1:1; the counter electrode is a sodium sheet, and they are assembled together to obtain a sodium ion battery.

[0066] Example 2

[0067] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0068] In this embodiment, the porous carbon precursor is microporous activated carbon ACF;

[0069] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:1;

[0070] In this embodiment, the heating rate of the carbonization process in step 2 is 10° C. / min, the heating temperature is 600° C., the holding time is 2 h, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 50 mL / min.

[0071] In this embodiment, the temperature of the standing process in step 3 is 80° C. and the standing time is 6 hours.

[0072] In this embodiment, the cooling rate of the cooling process in step 2 is 10°C / min, and the cooling end temperature is 30°C.

[0073] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0074] Example 3

[0075] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0076] In this embodiment, the porous carbon precursor is microporous activated carbon CEP21KSN;

[0077] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:0.02;

[0078] In this embodiment, the heating rate of the carbonization process in step 2 is 20° C. / min, the heating temperature is 800° C., the holding time is 0.1 h, the protective atmosphere is nitrogen, and the flow rate of the protective atmosphere is 10 mL / min.

[0079] In this embodiment, the temperature of the standing process in step 3 is 50° C. and the standing time is 6 hours.

[0080] In this embodiment, the cooling rate of the cooling process in step 2 is 20°C / min, and the cooling end temperature is 40°C.

[0081] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0082] Example 4

[0083] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0084] In this embodiment, the porous carbon precursor is hierarchical porous activated carbon, which is ground to a particle size of 1 μm;

[0085] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:1.5;

[0086] In this embodiment, the heating rate of the carbonization process in step 2 is 0.1°C / min, the heating temperature is 300°C, the holding time is 10h, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 20mL / min.

[0087] In this embodiment, the temperature of the standing process in step 3 is 50° C. and the standing time is 6 hours.

[0088] In this embodiment, the cooling rate of the cooling process in step 2 is 0.1°C / min, and the cooling end temperature is 10°C.

[0089] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0090] Example 5

[0091] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0092] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:2;

[0093] In this embodiment, the heating rate of the carbonization process in step 2 is 5° C. / min, the heating temperature is 800° C., and the holding time is 1 h.

[0094] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0095] Example 6

[0096] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0097] In this embodiment, the coating material is starch.

[0098] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:2.5;

[0099] In this embodiment, the heating rate of the carbonization process in step 2 is 15° C. / min, the heating temperature is 420° C., the holding time is 0.7 h, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 65 mL / min.

[0100] In this embodiment, the temperature of the standing process in step 3 is 80° C. and the standing time is 6 hours.

[0101] In this embodiment, the cooling rate of the cooling process in step 2 is 15°C / min, and the cooling end temperature is 35°C.

[0102] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0103] Example 7

[0104] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0105] In this embodiment, the coating material is phenolic resin carbon.

[0106] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:3;

[0107] In this embodiment, the heating rate of the carbonization process in step 2 is 8°C / min, the heating temperature is 720°C, the holding time is 1.5h, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 55mL / min.

[0108] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0109] Example 8

[0110] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0111] In this embodiment, the coating material is cyclodextrin.

[0112] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:3.5;

[0113] In this embodiment, the heating rate of the carbonization process in step 2 is 0.5°C / min, the heating temperature is 320°C, the holding time is 0.3h, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 35mL / min.

[0114] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0115] Example 9

[0116] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0117] In this embodiment, the coating material is piperazine pyrophosphate.

[0118] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:4;

[0119] In this embodiment, the heating rate of the carbonization process in step 2 is 3°C / min, the heating temperature is 450°C, the holding time is 7h, the protective atmosphere is ammonia and nitrogen, and the flow rate of the protective atmosphere is 45mL / min.

[0120] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0121] Example 10

[0122] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0123] In this embodiment, the coating material is chitosan.

[0124] In this embodiment, the mass ratio of porous carbon powder to coating material is 1:4.5;

[0125] In this embodiment, the heating rate of the carbonization process in step 2 is 16°C / min, the heating temperature is 700°C, the holding time is 5h, the protective atmosphere is ammonia and nitrogen, and the flow rate of the protective atmosphere is 85mL / min.

[0126] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0127] Example 11

[0128] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0129] In this embodiment, the phase change material is n-hexadecane.

[0130] In this embodiment, the mass ratio of the first coating layer material to the phase change material is 1:1.

[0131] In this embodiment, the temperature of the standing process in step 3 is 55° C. and the standing time is 7 hours.

[0132] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0133] Example 12

[0134] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0135] In this embodiment, the phase change material is n-octadecane.

[0136] In this embodiment, the mass ratio of the first coating layer material to the phase change material is 1:2.

[0137] In this embodiment, the temperature of the standing process in step 3 is 60° C. and the standing time is 8 hours.

[0138] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0139] Example 13

[0140] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0141] In this embodiment, the phase change material is fatty acid.

[0142] In this embodiment, the mass ratio of the first coating layer material to the phase change material is 1:1.5.

[0143] In this embodiment, the temperature of the standing process in step 3 is 65° C. and the standing time is 11 hours.

[0144] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0145] Example 14

[0146] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0147] In this embodiment, the phase change material is stearic acid.

[0148] In this embodiment, the mass ratio of the first coating layer material to the phase change material is 1:3.

[0149] In this embodiment, the temperature of the standing process in step 3 is 70° C. and the standing time is 10 h.

[0150] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0151] Example 15

[0152] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0153] In this embodiment, the phase change material is palmitic acid high-density polyethylene.

[0154] In this embodiment, the mass ratio of the first coating layer material to the phase change material is 1:4.

[0155] In this embodiment, the temperature of the standing process in step 3 is 75° C. and the standing time is 9 hours.

[0156] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0157] Example 16

[0158] The carbon material and preparation method of this embodiment are the same as those of Example 1, except that the raw materials and preparation process parameters are different:

[0159] In this embodiment, the phase change material is palmitic acid high-density polyethylene.

[0160] In this embodiment, the mass ratio of the first coating layer material to the phase change material is 1:5.

[0161] In this embodiment, the protective atmosphere during the heating and carbonization process in step 2 is hydrogen and nitrogen, and the flow rate of the protective atmosphere is 50 mL / min.

[0162] The assembly method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0163] Comparative Example 1

[0164] This comparative example provides a modified screening type carbon negative electrode material and a preparation method. Compared with Example 1, the difference is that this comparative example does not add phase change material for secondary coating process. The specific steps are:

[0165] 0.5 g of porous carbon powder (powder of activated petroleum coke AC-SYJ ground) and 2.5 g of coating material (glucose-derived carbon) were evenly mixed and ground, placed in a tubular furnace, and argon gas at a flow rate of 50 mL / min was introduced. The temperature was raised to 500 ° C at a rate of 5 ° C / min, and the reaction was kept at a constant temperature at 500 ° C for 1 hour. Then, the temperature was cooled to room temperature at a rate of 5 ° C / min to obtain a first coating layer material as a carbon material.

[0166] The obtained carbon material was used as the negative electrode active material to assemble a sodium ion battery, and the assembly method was the same as that in Example 1.

[0167] Comparative Example 2

[0168] This comparative example provides a modified screening type carbon negative electrode material and a preparation method. Compared with Example 1, the difference is that no coating material is added to the coating process in this comparative example. The specific steps are:

[0169] 0.5 g of porous carbon powder (powder of activated petroleum coke AC-SYJ ground) and 2.25 g of phase change material (paraffin) were uniformly mixed and ground, and allowed to stand at 50° C. for 12 h, and then cooled at room temperature and allowed to stand to obtain a carbon material.

[0170] The obtained carbon material was used as the negative electrode active material to assemble a sodium ion battery, and the assembly method was the same as that in Example 1.

[0171] Comparative Example 3

[0172] This comparative example provides a modified screening type carbon negative electrode material and a preparation method. Compared with Example 1, the difference is that this comparative example is not treated with a coating material and a phase change material, and the obtained carbon material is a porous carbon powder.

[0173] The obtained porous carbon powder is directly used as the negative electrode active material to assemble a sodium ion battery, and the assembly method is the same as that of Example 1.

[0174] Comparative Example 4

[0175] This comparative example provides a modified screening type carbon negative electrode material and a preparation method. Compared with Example 1, the difference is that the preparation process parameters are different:

[0176] The heating carbonization temperature of the heating carbonization process in step 2 of this comparative example is 250°C.

[0177] Comparative Example 5

[0178] This comparative example provides a modified screening type carbon negative electrode material and a preparation method. Compared with Example 1, the difference is that the preparation process parameters are different:

[0179] The heating carbonization temperature of the heating carbonization process in step 2 of this comparative example is 900°C.

[0180] Comparative Example 6

[0181] This comparative example provides a modified screening type carbon negative electrode material and a preparation method. Compared with Example 1, the difference is that the preparation process parameters are different:

[0182] In this comparative example, the cooling rate in step 2 is 25°C / min.

[0183] Test Example 1

[0184] The SEM spectra of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are as follows: Figure 1 、 Figure 5 、 Figure 9 and Figure 13 As shown, the particle size of the material was observed by scanning electron microscopy (SEM). From the SEM image at 10 um, it can be concluded that the particle size of the carbon materials obtained in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 is not much different, wherein: the primary particle size of the carbon material obtained in Example 1 is about 0.2 μm, and the secondary particle size is about 7 μm, the primary particle size of the carbon material obtained in Comparative Example 1 is about 0.5 μm, and the secondary particle size is about 10 μm, the primary particle size of the carbon material obtained in Comparative Example 2 is about 0.7 μm, and the secondary particle size is about 12 μm, and the primary particle size of the porous carbon powder obtained in Comparative Example 3 is about 0.5 μm, and the secondary particle size is about 10 μm.

[0185] Test Example 2

[0186] The carbon materials of Examples 1-16 and Comparative Examples 1-6 were subjected to nitrogen adsorption and desorption tests to obtain the corresponding specific surface area and average pore size distribution, as shown in Table 1. As can be seen from Table 1, compared with Comparative Examples 1-6, Examples 1-16 exhibited relatively small specific surface area and average pore size, which can effectively shorten the ion diffusion path, reduce the ion transmission resistance, and enable sodium ions to be embedded and extracted more quickly, thereby helping to improve the rate performance and rapid charge and discharge capability of the electrode.

[0187] The nitrogen (77K) adsorption / desorption curves of the carbon materials obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown as follows: Figure 2 、 6 , 10, and 14. The corresponding pore size distribution curves are shown as follows: Figure 3 、 7, 11 and 15, the distribution range of the pore size in the material can be intuitively known. The average pore size distribution of Example 1 is 0.8-2.4 nm, while the average pore size distribution of Comparative Example 1 is 1.5-3 nm, the average pore size distribution of Comparative Example 2 is 1.7-3 nm, and the average pore size distribution of Comparative Example 3 is 1.7-3 nm. At the same time, it can be seen that the pore size distribution of the material obtained in Example 1 is relatively concentrated and uniform, indicating that its ion transmission path is relatively uniform, which is beneficial to improving the capacity and rate performance of the battery, while Comparative Examples 1, 2, and 3 have multiple peaks, indicating that the pore size distribution of the obtained material is uneven, which will increase the complexity of the ion transmission path and lead to a decrease in battery performance.

[0188] Test Example 3

[0189] The sodium ion batteries assembled with the carbon materials of Examples 1-16 and Comparative Examples 1-6 were subjected to electrical performance tests. After the batteries were mounted on a test fixture, they were left standing at room temperature for 10 minutes to stabilize the battery state.

[0190] Charging settings: Charge the battery at a constant current of 0.1C. When the battery voltage reaches the set charge cut-off voltage (4.2V in this test example), switch to constant voltage charging mode. Constant voltage charging is continued until the current drops to 0.05C, at which point charging stops.

[0191] Discharge setting: After standing for 5 minutes, discharge the battery at a constant current of 0.1C. Stop discharging when the battery reaches the set discharge cut-off voltage (3.0V in this test example).

[0192] Then, the first cycle charge and discharge performance test and cycle performance test are carried out respectively. The test process is as follows:

[0193] 1. First cycle charge and discharge performance test:

[0194] Repeat the above charge and discharge steps for one cycle to observe the first-cycle charge and discharge specific capacity and first-cycle coulombic efficiency of the battery.

[0195] 2. Cyclic charge and discharge performance test:

[0196] Repeat the above charge and discharge steps for 5-10 cycles to observe the initial performance changes of the battery, and then conduct a long cycle test: based on the initial cycle test, continue to increase the number of cycles, record the charging capacity, discharge capacity, voltage curve and other data of each cycle, and stop the test when the discharge capacity of the battery is lower than 80% of the initial discharge capacity for two consecutive times.

[0197] The results are shown in Table 1:

[0198] Table 1 Performance test results of carbon materials

[0199]

[0200] From the results in Table 1, it can be seen that the first-cycle reversible capacity of the sodium ion battery obtained by using the double-layer coated carbon material of Examples 1-16 as the negative electrode material is between 300 and 490 mAh / g, the first coulombic efficiency can reach up to 93%, and it can be cycled 300-600 times when the capacity retention rate is 80%, with excellent comprehensive performance. Among them, Example 1 has the highest first-cycle reversible capacity (474 ​​mAh / g at 0.1C, 50 mA / g) and first coulombic efficiency (91%), and can operate stably for 600 cycles when the capacity retention rate is 80%, which is the optimal embodiment of this application.

[0201] The first cycle charge and discharge curve of Example 1 of the present invention is as follows: Figure 4 As shown, it can be seen that its first charge capacity is 474mAh / g, the first discharge capacity is 510mAh / g, and the first coulombic efficiency is calculated to be 93%; while the first cycle charge and discharge curve of comparative example 1 is as follows Figure 8 As shown, it can be seen that its first charge capacity is 248mAh / g, the first discharge capacity is 328mAh / g, and the first coulombic efficiency is calculated to be 76%; the first cycle charge and discharge curve of comparative example 2 is as follows Figure 12 As shown, it can be seen that its first charge capacity is 156mAh / g, the first discharge capacity is 191mAh / g, and the first coulombic efficiency is calculated to be 82%; the first cycle charge and discharge curve of comparative example 3 is as follows Figure 16 As shown, it can be seen that its first charge specific capacity is 85mAh / g, the first discharge specific capacity is 122mAh / g, and the calculated first coulombic efficiency is 69%.

[0202] The cyclic charge and discharge curves of Example 1 and Comparative Examples 1-3 are as follows Figure 17-20 As shown, compared with Example 1 ( Figure 17 ) compared with the results of comparative example 1 ( Figure 18 ), Comparative Example 2 ( Figure 19 ) and comparative example 3 ( Figure 20 ), all showed low first-cycle reversible capacity and first coulombic efficiency, poor cycle stability in the long cycle state, and when the capacity retention rate was 80%, the maximum cycle was only 296 cycles, resulting in poor overall performance, especially the sodium ion battery in Example 3 which directly used porous carbon powder as the negative electrode material, which could only cycle 197 cycles when the capacity retention rate was 80%.

[0203] From the comparison results of Example 1 and Comparative Examples 1-3, it can be seen that the carbon material prepared by the double-layer coating method in the embodiment of the present invention has a rich and regular pore structure and a uniformly distributed pore size. The carbon film formed by the first layer of coating material can provide a stable substrate for the second layer of phase change material. The uniform and dense carbon film can effectively protect the internal porous carbon material and prevent it from structural damage during subsequent treatment, so that it can be evenly distributed during the heat treatment process and form a second coating layer, which reduces the diffusion resistance of sodium ions, improves the transmission rate and efficiency of sodium ions, has good cycle stability, and significantly improves the overall performance of sodium ion batteries.

[0204] It can be seen from the results of Example 1 and Comparative Examples 4-6 that the parameter conditions of the preparation process will affect the final comprehensive performance. The comparison results of Comparative Example 4 and Example 1 show that if the heating carbonization temperature is low, the deposition rate will slow down, affecting the continuity of the internal pores, and thus affecting the rate performance of the material. The lower heating carbonization temperature will also lead to insufficient decomposition of the coating material, and it will be impossible to achieve sufficient coating of the porous carbon matrix, which will lead to a decrease in the first coulomb efficiency and a reduction in the platform capacity; the comparison results of Comparative Example 5 and Example 1 show that if the heating carbonization temperature is high, the coating material will be violently cracked, resulting in excessive deposition and an increase in ineffective energy consumption; the results of Comparative Example 6 and Example 1 show that if the cooling rate is too fast, it will lead to excessive coating, and the coating effect on the porous carbon matrix will be uncontrollable, reducing the low-potential platform capacity of the carbon material.

[0205] In summary, it can be concluded that the carbon film formed by first coating the first layer of coating material in the present invention can provide a stable substrate for the phase change material, so that it can be evenly distributed and form a second coating layer during the subsequent processing. This order can ensure that the material remains stable during the subsequent processing and realize the coordinated optimization of multiple functions. At the same time, this double-layer structure can realize the coordinated optimization of conductivity, thermal management and pore structure. The carbon film formed by the first layer of coating material at high temperature serves to provide protection for the internal structure. The rich internal pore structure and high conductivity can significantly improve the adsorption performance and electrochemical properties of the material. If the phase change material is coated first, it may melt or decompose prematurely during the high-temperature treatment process, resulting in the internal structure being exposed to the outside and unable to form a stable coating layer.

[0206] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention may be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the foregoing description. It is intended that all variations that fall within the meaning and range of equivalents of the claims be embraced within the present invention. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0207] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any minor modifications, equivalent replacements, and improvements made to the above embodiments based on the technical essence of the present invention shall be included in the scope of protection of the technical solution of the present invention.

Claims

1. A modified screening type carbon negative electrode material, obtained by coating the surface of porous carbon powder with a modified material, characterized in that: The modified material coating is a double layer coating of a coating material and a phase change material; wherein the coating material is coated on the surface of the porous carbon powder, and the phase change material is coated on the surface of the coating material; the porous carbon powder is obtained by grinding a porous carbon precursor; The phase change material is at least one of paraffin, n-hexadecane, n-octadecane, fatty acid, stearic acid, palmitic acid, high-density polyethylene, polyethylene glycol, alcohols, and lipids.

2. The modified screening type carbon negative electrode material according to claim 1, characterized in that: The coating material is at least one of glucose-derived carbon, phenolic resin carbon, starch, cyclodextrin, piperazine pyrophosphate, and chitosan; and the porous carbon precursor is at least one of microporous activated carbon, hierarchical porous activated carbon, template porous carbon, and porous graphene.

3. The modified screening type carbon negative electrode material according to claim 1, characterized in that: The modified carbon material has a particle size D50 of 1 to 20 μm, an average pore size of 0.1 to 5 nm, and a specific surface area of ​​4 to 100 m 2 / g.

4. A method for preparing the modified screening type carbon negative electrode material according to claim 1, characterized in that: The following steps are involved: Step 1: Grinding a porous carbon precursor to obtain a porous carbon powder having abundant nanopores inside; Step 2: uniformly mixing the porous carbon powder obtained in step 1 with the coating material and then grinding the mixture, subjecting the mixture to a heating and carbonization process, and cooling the mixture to obtain a first coating layer material; Step 3: uniformly mix the first coating layer material obtained in step 2 with the phase change material, grind the mixture, and allow to stand to obtain a modified carbon material.

5. The method for preparing the modified screening type carbon negative electrode material according to claim 4, characterized in that: The mass ratio of the porous carbon powder to the coating material is 1:(0.02-5); the mass ratio of the first coating layer material to the phase change material is 1:(0.02-10).

6. The method for preparing the modified screening type carbon negative electrode material according to claim 4, characterized in that: The porous carbon powder obtained in step 1 has a particle size D50 of 1 to 20 μm, an average pore size of 0.1 to 3 nm, and a specific surface area of ​​500 to 3000 m 2 / g.

7. The method for preparing the modified screening type carbon negative electrode material according to claim 4, characterized in that: The heating rate of the carbonization process in step 2 is 0.1-20°C / min, the heating temperature is 300-800°C, and the holding time is 0.1-10h; the cooling end temperature is 10-40°C, and the cooling rate is 0.1-20°C / min.

8. The method for preparing the modified screening type carbon negative electrode material according to claim 4, characterized in that: The standing temperature in step 3 is 50-80° C., and the standing time is 6-12 hours.

9. The method for preparing a modified screening type carbon negative electrode material according to claim 4, characterized in that: The heating carbonization process in step 2 is carried out in a protective atmosphere, wherein the protective atmosphere is at least one of argon, nitrogen, ammonia and hydrogen, and the flow rate of the protective atmosphere is 10 to 100 mL / min.

10. Use of the modified screening type carbon negative electrode material according to any one of claims 1 to 3 or the modified screening type carbon negative electrode material prepared by the preparation method according to any one of claims 4 to 9 in a sodium ion battery.

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