Phosphorus-carbon negative electrode material and preparation method thereof

Abstract

The invention provides a preparation method of a phosphorus-carbon negative electrode material, which comprises the following steps: step 1, hard carbon pretreatment: carrying out heat preservation treatment on hard carbon in a fluorine atmosphere to obtain a hard carbon material with high adsorbability; step 2, red phosphorus blending: placing the pretreated hard carbon material and red phosphorus in a closed container together, separately placing the hard carbon material and the red phosphorus, and vacuumizing the container to obtain a phosphorus-carbon material blended with the red phosphorus; and step 3, conducting polymer coating: putting the phosphorus-carbon material doped with the red phosphorus into a solution containing an aniline monomer, and adding an oxidizing agent to obtain a surface polyaniline coating layer so as to obtain the phosphorus-carbon negative electrode material. The invention also provides the phosphorus-carbon negative electrode material which is prepared by the preparation method. According to the phosphorus-carbon negative electrode material, the gram volume of the negative electrode material can be improved while sodium separation of a sodium-ion battery is relieved, good electrochemical stability is achieved, the preparation method is simple and rapid, and the phosphorus-carbon negative electrode material has very high market value.

Description

Technical Field

[0001] The present invention relates to the field of new materials and new energy technologies, and in particular to a negative electrode material capable of obtaining high specific capacity and low sodium precipitation risk and a preparation method thereof. Background Art

[0002] Currently, sodium-ion batteries (Na-ion batteries) are attracting significant attention due to their abundant sodium resources, economical cost, long cycle life, and excellent safety performance. Although still in the early stages of industrialization, Na-ion batteries have demonstrated significant potential in replacing lead-acid batteries and supplementing the lithium-ion battery market. With continued technological advancements and growing market demand, Na-ion batteries are expected to play an even more important role in future energy storage.

[0003] Hard carbon materials are considered to be the most promising option for rapid industrialization among current sodium-ion battery negative electrode materials due to their wide range of raw materials, simple synthesis methods, relatively low cost, and good theoretical gram capacity. The discharge curve of hard carbon materials is usually composed of a slope region and a platform region. Material manufacturers generally increase the overall gram capacity by increasing the proportion of the platform region of hard carbon materials. However, the platform region voltage of hard carbon is around 100mV. When polarization occurs during high-rate charging or long-term cycling, sodium precipitation is very likely to occur, consuming electrolyte and causing a decrease in battery capacity. Therefore, hard carbon negative electrodes face the dilemma of being unable to achieve both high capacity and low sodium precipitation risk.

[0004] Among various anode materials, red phosphorus (RP) has gained widespread attention due to its ultra-high theoretical capacity (2596 mAh / g for Na3P) and low cost. Furthermore, with a redox potential of approximately 0.4 V (vs Na / Na+), its operating potential as a cathode material is significantly higher than the precipitation potential of sodium ions, effectively preventing sodium precipitation during use. However, red phosphorus has poor conductivity and significantly expands during charge and discharge, making it unsuitable for use as a standalone anode material.

[0005] Therefore, how to obtain negative electrode materials with high specific capacity and low sodium precipitation risk is an urgent problem that the sodium-ion battery industry needs to solve. Summary of the Invention

[0006] A main purpose of the present invention is to overcome at least one of the defects of the above-mentioned prior art and provide a phosphorus-carbon negative electrode material and a preparation method thereof that can obtain a negative electrode material with high specific capacity and low sodium precipitation risk.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] According to one aspect of the present invention, there is provided a method for preparing a phosphorus-carbon negative electrode material, comprising:

[0009] Step 1, hard carbon pretreatment: heat-treating the hard carbon in a fluorine atmosphere to obtain a hard carbon material with high adsorption capacity;

[0010] Step 2, red phosphorus blending: placing the pretreated hard carbon material and red phosphorus together in a sealed container, placing the two separately, and evacuating the container to obtain a red phosphorus-blended phosphorus-carbon material;

[0011] Step 3, conductive polymer coating: placing the phosphorus-carbon material mixed with red phosphorus in a solution containing aniline monomer, adding an oxidant to obtain a surface polyaniline coating layer, thereby obtaining a phosphorus-carbon negative electrode material.

[0012] According to a specific embodiment of the present invention, in step 1, the fluorine atmosphere is a mixture of fluorine with a concentration of 5%-15% and an inert gas, and the inert gas is any one of nitrogen, argon, and helium, or any combination thereof.

[0013] According to a specific embodiment of the present invention, in step 1, the temperature range of the insulation treatment is 25-80° C., and the treatment time is 1-8 hours.

[0014] According to a specific embodiment of the present invention, in step 2, the temperature is raised to 800-1000° C. and maintained for 24 hours, and then cooled to room temperature.

[0015] According to a specific embodiment of the present invention, in step 2, the mass ratio of hard carbon to red phosphorus is 1:(0.01-0.3).

[0016] According to a specific embodiment of the present invention, in step 2, the particle size D50 of the hard carbon material is 4-6 μm, and the specific surface area is 3-6 m 2 / g, tap density 0.7-1g / cm 3 .

[0017] According to a specific embodiment of the present invention, in step 2, the particle size D50 of the hard carbon material is 5.1 μm, and the specific surface area is 4.9 m 2 / g, tap density 0.8g / cm 3 .

[0018] According to a specific embodiment of the present invention, in step 3, the oxidant is ammonium persulfate, and the pH value of the solution is 2 to 3.5.

[0019] According to a specific embodiment of the present invention, in step 3, the phosphorus-carbon material is stirred in the solution for 12 hours, and then the phosphorus-carbon material is filtered and dried.

[0020] According to another aspect of the present invention, a phosphorus-carbon negative electrode material is provided, which is prepared by the above-mentioned preparation method.

[0021] As can be seen from the above technical solutions, the advantages and positive effects of the phosphorus-carbon negative electrode material and the preparation method thereof of the present invention are:

[0022] The phosphorus-carbon negative electrode material of the present invention can improve the gram capacity of the negative electrode material while alleviating sodium precipitation in sodium ion batteries, and has good electrochemical stability. The preparation method is simple and fast, and has very high market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the surface morphology of the phosphorus-carbon material in Example 1.

[0024] Figure 2 This is a schematic diagram of the element distribution on the surface of the phosphorus-carbon material in Example 1.

[0025] Figure 3 Schematic diagram of half-cell charge and discharge curves of Example 1 and Comparative Example 1.

[0026] Figure 4 This is a schematic diagram of rate discharge performance of Example 1.

[0027] Figure 5 Schematic diagram of the cycle performance of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0028] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the figures represent like or similar structures, and thus their detailed description will be omitted.

[0029] In the following description of different examples of the present invention, reference is made to the accompanying drawings, which form a part of the present invention and in which are shown by way of example different exemplary structures, systems and steps that can implement aspects of the present invention. It will be understood that other specific schemes of components, structures, exemplary devices, systems and steps can be used, and structural and functional modifications can be made without departing from the scope of the present invention. Moreover, although the terms "top", "bottom", "front", "rear", "side" and the like may be used in this specification to describe different exemplary features and elements of the present invention, these terms are used herein for convenience only, for example according to the orientation of the examples described in the accompanying drawings. Nothing in this specification should be construed as requiring a specific three-dimensional orientation of the structure to fall within the scope of the present invention.

[0030] The following is an explanation of the professional terms used in the claims and description of the present invention.

[0031] 1. Particle size distribution parameter D50: The equivalent particle size value when the cumulative volume distribution percentage is 50%, which characterizes the average particle size of the material.

[0032] 2. Specific surface area (BET Surface Area)

[0033] Definition: Surface area per unit mass of material (unit: m 2 / g), as measured by the nitrogen adsorption BET method (GB / T 19587-2017). A high specific surface area can accelerate ion transport, but it can easily lead to electrolyte decomposition side reactions, reducing coulombic efficiency.

[0034] In a specific technical solution of the present invention, the following method for preparing phosphorus-carbon negative electrode material is adopted.

[0035] 1. Hard carbon pretreatment: The hard carbon is kept in a fluorine atmosphere for a period of time to obtain a hard carbon material A with high adsorption capacity;

[0036] The fluorine atmosphere is a mixture of fluorine with a concentration of 5%-15% and an inert gas, and the inert gas can be one or more of nitrogen, argon, and helium; the temperature range of the heat preservation treatment is 25-80

[0037] ℃, processing time 1-8h.

[0038] 2. Red phosphorus blending: The pretreated hard carbon material A and red phosphorus are placed together in a sealed container, the two are separated, the container is evacuated, and the temperature is raised to a certain level and maintained for 24 hours, and then cooled to room temperature to obtain a red phosphorus-blended phosphorus-carbon material B;

[0039] The mass ratio of hard carbon to red phosphorus is 1:0.01-0.3, and the holding temperature is 800-1000°C. The hard carbon material is model SQPNHC-2A, with a particle size D50 of 5.1 μm and a BET specific surface area of 4.9 m 2 / g, tap density 0.8g / cm 3 .

[0040] 3. Conductive polymer coating:

[0041] The phosphorus-carbon negative electrode material is placed in a solution containing aniline monomer, an oxidant such as ammonium persulfate is added, the pH value is adjusted to 2-3.5, stirred for 12 hours, filtered and dried to obtain a surface polyaniline coating layer.

[0042] Example 1

[0043] A method for preparing a phosphorus-carbon negative electrode material comprises:

[0044] S1: heat-treating hard carbon in a 5% fluorine atmosphere at 50°C for 4 hours to obtain a hard carbon material with high adsorption capacity;

[0045] S2: placing the above materials together with red phosphorus in a sealed container, heating to 900°C at a rate of 5°C / min for heat treatment, maintaining for 24 hours and then naturally cooling to room temperature, the mass ratio of hard carbon to red phosphorus being 1:0.05;

[0046] S3: placing the product obtained in the previous step into a solution containing aniline monomer, adding ammonium persulfate, adjusting the pH value to 2.5, stirring for 12 hours, filtering and drying to obtain a phosphorus-carbon material with a polyaniline coating layer on the surface.

[0047] A method for manufacturing a sodium ion battery, wherein the negative electrode plate is made of the above-mentioned phosphorus-carbon negative electrode material and the positive electrode material is a layered oxygen material (sodium nickel iron manganese oxide):

[0048] A1: Prepare a slurry of phosphorus-carbon composite material, conductive carbon black, CNT slurry, sodium carboxymethyl cellulose and styrene-butadiene rubber in a ratio of 93.7wt%:1.5wt%:0.5wt%:1.5wt%:2.8wt%. The solvent is deionized water and a small amount of NMP. Adjust the viscosity of the negative electrode slurry to 3000-5000mPa·s.

[0049] A2: The prepared slurry is coated on aluminum foil with a negative electrode double-sided density of 340g / m2. After coating and baking, the negative electrode sheet is obtained by roller pressing and slitting.

[0050] A3: The positive and negative electrodes are wound and packaged with a protective coating separator, then vacuum-baked at 90°C until the moisture content is less than 300 ppm. After passing the baking test, a high-temperature resistant electrolyte is injected. The finished battery is then subjected to high-temperature aging, formation, high-temperature aging, and capacity separation.

[0051] Example 2

[0052] A method for preparing a phosphorus-carbon negative electrode material comprises:

[0053] S1: heat-treating hard carbon in a 5% fluorine atmosphere at 80°C for 6 hours to obtain a hard carbon material with high adsorption capacity;

[0054] S2: placing the above materials together with red phosphorus in a sealed container, heating to 900°C at a rate of 5°C / min for heat treatment, maintaining for 24 hours and then naturally cooling to room temperature, the mass ratio of hard carbon to red phosphorus being 1:0.05;

[0055] S3: placing the product obtained in the previous step into a solution containing aniline monomer, adding ammonium persulfate, adjusting the pH value to 2.5, stirring for 12 hours, filtering and drying to obtain a phosphorus-carbon material with a polyaniline coating layer on the surface.

[0056] A method for manufacturing a sodium ion battery, same as that of Example 1.

[0057] Example 3

[0058] A method for preparing a phosphorus-carbon negative electrode material comprises:

[0059] S1: heat-treating hard carbon in a 5% fluorine atmosphere at 50°C for 4 hours to obtain a hard carbon material with high adsorption capacity;

[0060] S2: Place the above materials together with red phosphorus in a sealed container, heat treat at a rate of 5°C / min to 800°C, maintain for 24 hours, and then cool naturally to room temperature. The mass ratio of hard carbon to red phosphorus is 1:0.1;

[0061] S3: placing the product obtained in the previous step into a solution containing aniline monomer, adding ammonium persulfate, adjusting the pH value to 2.5, stirring for 12 hours, filtering and drying to obtain a phosphorus-carbon material with a polyaniline coating layer on the surface.

[0062] A method for manufacturing a sodium ion battery, same as that of Example 1.

[0063] Example 4

[0064] A method for preparing a phosphorus-carbon negative electrode material comprises:

[0065] S1: heat-treating hard carbon in a 5% fluorine atmosphere at 80°C for 6 hours to obtain a hard carbon material with high adsorption capacity;

[0066] S2: placing the above materials together with red phosphorus in a sealed container, heating to 1000°C at a rate of 5°C / min for heat treatment, maintaining for 24 hours and then naturally cooling to room temperature, the mass ratio of hard carbon to red phosphorus being 1:0.25;

[0067] S3: placing the product obtained in the previous step into a solution containing aniline monomer, adding ammonium persulfate, adjusting the pH value to 2.5, stirring for 12 hours, filtering and drying to obtain a phosphorus-carbon material with a polyaniline coating layer on the surface.

[0068] A method for manufacturing a sodium ion battery, same as that of Example 1.

[0069] Example 5

[0070] A method for preparing a phosphorus-carbon negative electrode material comprises:

[0071] S1: The hard carbon is treated in a 10% fluorine atmosphere at 35°C for 2 hours to obtain a hard carbon material with high adsorption capacity;

[0072] S2: placing the above materials together with red phosphorus in a sealed container, heating to 900°C at a rate of 5°C / min for heat treatment, maintaining for 24 hours and then naturally cooling to room temperature, the mass ratio of hard carbon to red phosphorus being 1:0.05;

[0073] S3: placing the product obtained in the previous step into a solution containing aniline monomer, adding ammonium persulfate, adjusting the pH value to 2.5, stirring for 12 hours, filtering and drying to obtain a phosphorus-carbon material with a polyaniline coating layer on the surface.

[0074] A method for manufacturing a sodium ion battery, same as that of Example 1.

[0075] Comparative Example 1

[0076] A method for manufacturing a sodium ion battery, wherein the negative electrode plate is made of a hard carbon negative electrode material:

[0077] S1: Prepare a slurry of hard carbon material, conductive carbon black, CNT slurry, sodium carboxymethyl cellulose and styrene-butadiene rubber in a ratio of 93.7wt%:1.5wt%:0.5wt%:1.5wt%:2.8wt% using deionized water and a small amount of NMP as the solvent. Adjust the viscosity of the negative electrode slurry to 3000-5000mPa·s.

[0078] S2: The prepared slurry is coated on aluminum foil with a negative electrode double-sided density of 340 g / m2. After coating and baking, the negative electrode sheet is obtained by rolling and slitting.

[0079] S3: The positive and negative electrode sheets are wound and packaged with a protective coating separator, and then vacuum-baked at 90°C until the moisture content is less than 300ppm. After passing the baking test, a high-temperature resistant electrolyte is injected, and the finished battery is obtained after high-temperature aging, formation, high-temperature aging, and capacity separation.

[0080] Comparative Example 2

[0081] A method for preparing a phosphorus-carbon negative electrode material comprises:

[0082] S1: placing the hard carbon material and red phosphorus together in a sealed container, heating the temperature to 900°C at a heating rate of 5°C / min for heat treatment, maintaining the temperature for 24 hours, and then naturally cooling to room temperature. The mass ratio of hard carbon to red phosphorus is 1:0.05;

[0083] S2: placing the product obtained in the previous step into a solution containing aniline monomer, adding ammonium persulfate, adjusting the pH value to 2.5, stirring for 12 hours, filtering and drying to obtain a phosphorus-carbon material with a polyaniline coating layer on the surface.

[0084] A method for manufacturing a sodium ion battery, same as that of Example 1.

[0085]

[0086] Table 1: Comparison of test results for each case

[0087] As can be seen from Table 1, when Example 1 is compared with Comparative Example 3, it can be seen that the lack of fluorination treatment results in a limited amount of red phosphorus incorporated, and the capacity improvement is not obvious; and when Example 1 is compared with Example 5, it can be seen that a too short fluorination time may lead to uneven fluorination of the material surface, resulting in local areas of insufficient modification or unmodified areas, thereby affecting the phosphorus incorporation effect; when the treatment time is too long (Compared with Example 2), the material surface may be excessively fluorinated, resulting in damage to the surface structure of the material and affecting the material performance. At the same time, when Example 1 is compared with Comparative Example 2, the surface coating polymer layer can limit the volume expansion of the phosphorus element during the charge and discharge process, thereby improving the stability of the battery. It can be verified from Example 1 compared with Examples 4 and 5 that due to the poor conductivity and large volume expansion rate of phosphorus, the red phosphorus doping amount is preferably around 5%. Too high a level will cause a significant decrease in the stability of the battery.

[0088] Figure 1 This is the surface morphology of the phosphorus-carbon material. It can be seen that small particles of red phosphorus are dispersed on large particles of hard carbon, which can shorten the sodium ion transmission path. Figure 2 The four figures are a group, showing the distribution of elements on the surface of the phosphorus-carbon material (gray is the surface morphology, and the remaining three are the element distribution corresponding to the position, red C, green O, blue P), which shows that through the method of the present invention, red phosphorus can be evenly compounded in the hard carbon material. Figure 1 and Figure 2 It can be seen that through the method of the present invention, red phosphorus can be evenly compounded in the hard carbon material.

[0089] from Figure 3 It can be seen that:

[0090] A. The reversible specific capacity of pure hard carbon before compounding is 312 mAh / g, while the reversible specific capacity of the phosphorus-carbon anode compounded with 5% red phosphorus can reach over 365 mAh / g, with an initial efficiency of over 91%. This shows that the addition of a certain amount of phosphorus can effectively increase the specific capacity of the anode material.

[0091] B. Before compounding, the capacity of pure hard carbon material when discharged to 100mV accounted for about 23%; after compounding, the capacity of phosphorus-carbon material when discharged to 100mV accounted for 41%, which indicates that the capacity proportion of the slope area of phosphorus-carbon negative electrode material increased. The addition of red phosphorus makes the sodium storage potential curve rise as a whole, which can effectively mitigate the risk of sodium desorption.

[0092] from Figure 4 It can be seen from the figure that even though red phosphorus with poor conductivity is mixed in Example 1, the phosphorus-carbon material synthesized by the preparation method of the present invention still has good rate discharge performance in practical applications.

[0093] from Figure 5 It can be seen that Example 1 has better cycle performance.

[0094] Those skilled in the art will appreciate that the specific structures and processes described in the above detailed embodiments are merely illustrative and non-limiting. Furthermore, those skilled in the art may combine the various technical features described above in various possible ways to create new technical solutions or make other modifications, all of which fall within the scope of the present invention.

Claims

1. A method for preparing a phosphorus-carbon negative electrode material, characterized in that: include: Step 1, hard carbon pretreatment: heat-treating the hard carbon in a fluorine atmosphere to obtain a hard carbon material with high adsorption capacity; Step 2, red phosphorus blending: placing the pretreated hard carbon material and red phosphorus together in a sealed container, placing the two separately, and evacuating the container to obtain a red phosphorus-blended phosphorus-carbon material; Step 3, conductive polymer coating: placing the phosphorus-carbon material mixed with red phosphorus in a solution containing aniline monomer, adding an oxidant to obtain a surface polyaniline coating layer, thereby obtaining a phosphorus-carbon negative electrode material.

2. The method for preparing the phosphorus-carbon negative electrode material according to claim 1, wherein: In step 1, the fluorine atmosphere is a mixture of fluorine with a concentration of 5% to 15% and an inert gas, and the inert gas is any one of nitrogen, argon, and helium, or any combination thereof.

3. The method for preparing the phosphorus-carbon negative electrode material according to claim 2, wherein: In step 1, the temperature range of the insulation treatment is 25-80° C., and the treatment time is 1-8 hours.

4. The method for preparing the phosphorus-carbon negative electrode material according to claim 1, wherein: In the step 2, the temperature is raised to 800-1000° C. and maintained for 24 hours, and then cooled to room temperature.

5. The method for preparing the phosphorus-carbon negative electrode material according to claim 4, characterized in that: In the step 2, the mass ratio of hard carbon to red phosphorus is 1:(0.01-0.3).

6. The method for preparing the phosphorus-carbon negative electrode material according to claim 5, characterized in that: In step 2, the particle size D50 of the hard carbon material is 4-6 μm, and the specific surface area is 3-6 m 2 / g, tap density 0.7-1g / cm 3 .

7. The method for preparing the phosphorus-carbon negative electrode material according to claim 6, characterized in that: In step 2, the particle size D50 of the hard carbon material is 5.1 μm and the specific surface area is 4.9 m 2 / g, tap density 0.8g / cm 3 .

8. The method for preparing the phosphorus-carbon negative electrode material according to claim 1, wherein: In step 3, the oxidant is ammonium persulfate, and the pH value of the solution is 2 to 3.

5.

9. The method for preparing the phosphorus-carbon negative electrode material according to claim 1 or 8, characterized in that: In the step 3, the phosphorus-carbon material is stirred in the solution for 12 hours, and then the phosphorus-carbon material is filtered and dried.

10. A phosphorus-carbon negative electrode material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

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