A hard carbon-phosphorus composite negative electrode material and its preparation method and sodium ion battery

Abstract

The present invention provides a hard carbon-phosphorus composite negative electrode material and its preparation method and sodium ion battery, relating to the technical field of sodium ion batteries; the preparation method comprises the following steps: under an inert atmosphere, white phosphorus and a carbon source are mixed and dissolved in a solvent to obtain a mixed solution; a catalyst is added to the mixed solution to obtain a reaction solution; the reaction solution is heated at 50°C to obtain a mixture; the mixture is placed in a closed pressure reactor, heated to 500-600°C for reaction for 1 hour to obtain a solid product; the solid product is crushed to obtain a hard carbon-phosphorus composite negative electrode material. The preparation method of the hard carbon-phosphorus composite negative electrode material provided by the present invention uses white phosphorus and a carbon source as raw materials, and under the action of a catalyst, white phosphorus is in situ generated into nano red phosphorus particles in the carbon source, thereby improving the cycle performance of the composite negative electrode material while improving the specific capacity of the composite negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a hard carbon-phosphorus composite negative electrode material and a preparation method thereof, and a sodium ion battery. Background Art

[0002] Hard carbon is a commercialized negative electrode material for sodium-ion batteries, with advantages such as small volume expansion during charge and discharge and long cycle life. However, the current capacity of hard carbon materials is generally no higher than 350 mAh / g, which restricts the improvement of the energy density of sodium-ion batteries. Phosphorus (P) as a negative electrode material for sodium-ion batteries has a high specific capacity (2595 mAh / g), but phosphorus has poor conductivity and, after forming an alloy with sodium, has an excessively high expansion rate, easily pulverizing during the cycle, resulting in poor battery cycle performance. Therefore, the use of carbon materials and phosphorus to form a composite is an effective method to improve the cycle performance of sodium-ion batteries.

[0003] Phosphorus has three isotropes: white phosphorus, red phosphorus, and black phosphorus. White phosphorus is active and easily self-ignites in the air. If it is directly used as the negative electrode material of sodium-ion batteries, it poses a major safety hazard. The chemical properties of red phosphorus and black phosphorus are relatively stable, but the preparation of black phosphorus mostly requires high temperature and high pressure conditions. Therefore, the composite of carbon materials and red phosphorus is the current research focus.

[0004] In order to ensure the electrochemical performance of carbon-phosphorus composite materials and alleviate the volume expansion and contraction of red phosphorus during charging and discharging, red phosphorus needs to be nano-sized. In the existing preparation process of hard carbon-phosphorus composite negative electrode materials, commercially purchased red phosphorus is usually used as the raw material, and red phosphorus and hard carbon are ball-milled to obtain nano-sized red phosphorus and hard carbon composite materials. However, in the composite materials prepared by this method, the red phosphorus particles are easily agglomerated and have poor dispersion uniformity, resulting in poor cycle performance of the composite negative electrode material. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: in order to solve the problem of poor uniformity of red phosphorus particle dispersion in the prior art, the present invention provides a method for preparing a hard carbon-phosphorus composite negative electrode material. The preparation method uses white phosphorus and a carbon source as raw materials. After mixing the white phosphorus and the carbon source, the white phosphorus is directly converted into nano red phosphorus particles in the mixture with the carbon source under the action of a catalyst, so that the prepared nano red phosphorus particles are uniformly dispersed in the carbon source. After carbonization, a hard carbon-phosphorus composite negative electrode material with uniformly distributed nano red phosphorus particles is obtained, thereby solving the problem of poor uniformity of red phosphorus particle dispersion in the prior art.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A method for preparing a hard carbon-phosphorus composite negative electrode material comprises the following steps:

[0008] S1: Under an inert atmosphere, white phosphorus and a carbon source are mixed and dissolved in a solvent to obtain a mixed solution;

[0009] S2: adding a catalyst to the mixed solution to obtain a reaction solution;

[0010] S3: heating the reaction solution at 50° C. to obtain a mixture;

[0011] S4: placing the mixture in a sealed pressure reactor, heating to 500-600° C. and reacting for 1 hour to obtain a solid product;

[0012] S5: crushing the solid product to obtain a hard carbon-phosphorus composite negative electrode material.

[0013] Optionally, the catalyst is ethylenediamine.

[0014] Optionally, the carbon source is resin.

[0015] Optionally, the resin is selected from at least one of phenolic resin, epoxy resin, and urea-formaldehyde resin.

[0016] Optionally, the solvent is carbon disulfide.

[0017] Optionally, the usage ratio of the white phosphorus, the carbon source, the catalyst, and the solvent is 1 g: (20-50) g: (0.1-0.8) mL: (50-100) mL.

[0018] Optionally, the heating method in step S3 is water bath heating.

[0019] Optionally, the heating rate in step S4 is (5-10)°C / min.

[0020] Another object of the present invention is to provide a hard carbon-phosphorus composite negative electrode material, which is prepared by the above-mentioned method for preparing the hard carbon-phosphorus composite negative electrode material.

[0021] Another object of the present invention is to provide a sodium ion battery comprising the hard carbon-phosphorus composite negative electrode material as described above.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a method for preparing a hard carbon-phosphorus composite negative electrode material. White phosphorus and a carbon source are used as raw materials. Under the action of a catalyst, the white phosphorus generates nano red phosphorus particles in situ in the carbon source. This ensures that the nano red phosphorus particles are uniformly distributed in the carbon source while also ensuring the uniformity of the particle size distribution of the nano red phosphorus particles. This further ensures the uniformity of the particle size distribution of the nano red phosphorus particles in the prepared composite negative electrode material and the uniformity of the distribution of the nano red phosphorus particles in the hard carbon. This ensures the uniformity of the performance of the composite negative electrode material, improves the specific capacity of the composite negative electrode material, and improves the cycle performance of the composite negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and examples.

[0025] Figure 1 This is a TEM photograph of the hard carbon-phosphorus composite negative electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0027] In order to solve the problem of poor dispersion uniformity of red phosphorus particles in the prior art, the present invention provides a method for preparing a hard carbon-phosphorus composite negative electrode material, which comprises the following steps:

[0028] S1: Under an inert atmosphere, white phosphorus and a carbon source are mixed and dissolved in a solvent to obtain a mixed solution;

[0029] S2: adding a catalyst to the mixed solution to obtain a reaction solution;

[0030] S3: heating the reaction solution at 50° C. to obtain a mixture;

[0031] S4: placing the mixture in a sealed pressure reactor, heating to 500-600°C and reacting for 1 hour to obtain a solid product;

[0032] S5: crushing the solid product to obtain a hard carbon-phosphorus composite negative electrode material.

[0033] Due to the active nature of white phosphorus, the preparation method provided by the present invention needs to be carried out under an inert atmosphere, preferably under a nitrogen atmosphere. Specifically, the present invention first mixes white phosphorus and a carbon source, dissolves the mixture in a solvent, and stirs the mixture to ensure that the white phosphorus and the carbon source are fully and evenly mixed. Then, a catalyst is added, the mixture is heated, and the solvent is removed. Under the action of the catalyst, the white phosphorus is in situ converted into nano red phosphorus particles in the carbon source. On the one hand, the nano red phosphorus particles can be evenly dispersed in the carbon source. On the other hand, because the red phosphorus in the present invention is directly converted from white phosphorus, the particle size distribution of the nano red phosphorus particles is more uniform compared to the nano red phosphorus obtained by the traditional ball milling method. The nano-sized red phosphorus particles are directly generated in the carbon source and are therefore not prone to agglomeration, thereby helping to further ensure the uniformity of the distribution of the nano-red phosphorus particles in the carbon source. A mixture consisting of the carbon source and the nano-red phosphorus particles uniformly distributed therein is heated to 500-600° C. in a closed pressure reactor and reacted for 1 hour, whereby the carbon source is decomposed and carbonized to form hard carbon, thereby obtaining a solid product. The solid product is then crushed and sieved to obtain a hard carbon-phosphorus composite negative electrode material in which the nano-red phosphorus particles have a uniform particle size distribution and are uniformly distributed in the hard carbon. This can improve the specific capacity of the negative electrode material while also improving the cycle performance of the negative electrode material.

[0034] The present invention provides a method for preparing a hard carbon-phosphorus composite negative electrode material. White phosphorus and a carbon source are used as raw materials. Under the action of a catalyst, the white phosphorus generates nano red phosphorus particles in situ in the carbon source. This ensures that the nano red phosphorus particles are uniformly distributed in the carbon source while also ensuring the uniformity of the particle size distribution of the nano red phosphorus particles. This further ensures the uniformity of the particle size distribution of the nano red phosphorus particles in the prepared composite negative electrode material and the uniformity of the distribution of the nano red phosphorus particles in the hard carbon. This ensures the uniformity of the performance of the composite negative electrode material, improves the specific capacity of the composite negative electrode material, and improves the cycle performance of the composite negative electrode material.

[0035] In order to convert white phosphorus into nano red phosphorus particles in situ in a carbon source, the preferred catalyst of the present invention is ethylenediamine.

[0036] The present invention further prefers that the carbon source is a resin, so that after the catalyst ethylenediamine is added, white phosphorus is converted into nano-red phosphorus particles. At the same time, due to the presence of the organic base ethylenediamine, the resin is promoted to solidify, so that the generated nano-red phosphorus particles are in situ dispersed in the solidified resin; the solidified resin will not undergo melting deformation during the subsequent carbonization process, which is conducive to maintaining the uniform distribution of the nano-red phosphorus particles in the hard carbon, and helps to ensure the cycle performance of the composite negative electrode material.

[0037] Furthermore, the present invention preferably uses at least one resin selected from phenolic resin, epoxy resin, and urea-formaldehyde resin, and more preferably uses epoxy resin.

[0038] The preferred solvent of the present invention is carbon disulfide.

[0039] In order to take into account both reaction conversion rate and economy, the present invention preferably uses white phosphorus, carbon source, catalyst, and solvent in a ratio of 1 g: (20-50) g: (0.1-0.8) mL: (50-100) mL.

[0040] To ensure the safety of the reaction and the electrochemical performance of the composite negative electrode material, the preferred heating method in step S3 of the present invention is water bath heating; the preferred heating rate in step S4 is (5-10)°C / min.

[0041] Another object of the present invention is to provide a hard carbon-phosphorus composite negative electrode material, which is prepared by the preparation method of the hard carbon-phosphorus composite negative electrode material as described above.

[0042] The hard carbon-phosphorus composite negative electrode material provided by the present invention uses white phosphorus and a carbon source as raw materials during the preparation process. Under the action of a catalyst, the white phosphorus generates nano red phosphorus particles in situ in the carbon source. Thus, while ensuring the uniformity of the distribution of the nano red phosphorus particles in the carbon source, the uniformity of the particle size distribution of the nano red phosphorus particles is ensured. This further ensures the uniformity of the particle size distribution of the nano red phosphorus particles in the prepared composite negative electrode material and the uniformity of the distribution of the nano red phosphorus particles in the hard carbon, thereby ensuring the uniformity of the performance of the composite negative electrode material, and improving the cycle performance of the composite negative electrode material while improving the specific capacity of the composite negative electrode material.

[0043] Another object of the present invention is to provide a sodium ion battery, which includes the hard carbon-phosphorus composite negative electrode material as described above.

[0044] The sodium ion battery provided by the present invention uses a hard carbon-phosphorus composite negative electrode material as the negative electrode. During the preparation process of the hard carbon-phosphorus composite negative electrode material, white phosphorus and a carbon source are used as raw materials. Under the action of a catalyst, the white phosphorus generates nano red phosphorus particles in situ in the carbon source. Thus, while ensuring the uniformity of the distribution of the nano red phosphorus particles in the carbon source, the uniformity of the particle size distribution of the nano red phosphorus particles is ensured. In addition, the uniformity of the particle size distribution of the nano red phosphorus particles in the prepared composite negative electrode material and the uniformity of the distribution of the nano red phosphorus particles in the hard carbon are ensured, thereby ensuring the uniformity of the performance of the composite negative electrode material. While improving the specific capacity of the composite negative electrode material, the cycle performance of the composite negative electrode material is also improved, thereby obtaining a sodium ion battery with excellent long cycle life characteristics.

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0046] Example 1

[0047] This embodiment provides a method for preparing a hard carbon-phosphorus composite negative electrode material, comprising the following steps:

[0048] S1: Under nitrogen atmosphere, mix 1 g of white phosphorus and 35 g of epoxy resin, dissolve in 80 mL of carbon disulfide solvent, and stir to obtain a mixed solution;

[0049] S2: Add 0.5 mL of catalyst ethylenediamine to the mixed solution and stir evenly to obtain a reaction solution;

[0050] S3: The reaction solution was placed in a beaker and heated in a 50°C water bath for 120 min to remove carbon disulfide to obtain a mixture;

[0051] S4: placing the mixture in a sealed pressure reactor, heating it to 550°C at a heating rate of 8°C / min and reacting it for 1 hour, wherein the epoxy resin is decomposed and carbonized into hard carbon to obtain a solid product;

[0052] S5: The solid product was crushed and passed through a 325-mesh sieve to obtain a hard carbon-phosphorus composite negative electrode material.

[0053] The performance of the prepared hard carbon-phosphorus composite negative electrode material was tested, and its TEM image is shown in Figure 1 As shown, the dark particles are phosphorus.

[0054] Example 2

[0055] The difference between this embodiment and embodiment 1 is that the amount of epoxy resin added in step S1 is 20 g.

[0056] Example 3

[0057] The difference between this embodiment and embodiment 1 is that the amount of epoxy resin added in step S1 is 50 g.

[0058] Example 4

[0059] The difference between this embodiment and embodiment 1 is that the resin in step S1 is phenolic resin.

[0060] Example 5

[0061] The difference between this embodiment and embodiment 1 is that the resin in step S1 is urea-formaldehyde resin.

[0062] Example 6

[0063] The difference between this embodiment and embodiment 1 is that the resin in step S1 is a mixture of epoxy resin and urea-formaldehyde resin in a mass ratio of 1:1.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a negative electrode material, comprising the following steps:

[0066] Using epoxy resin as the carbon source, 36 g of epoxy resin was placed in a pressure reactor and heated to 550°C at a heating rate of 8°C / min for 1 hour. The epoxy resin was decomposed and carbonized into hard carbon, which was crushed and passed through a 325-mesh sieve to obtain the negative electrode material.

[0067] Comparative Example 2

[0068] This comparative example provides a method for preparing a negative electrode material, comprising the following steps:

[0069] Under a nitrogen atmosphere, 36 g of white phosphorus was placed in a pressure reactor, and the temperature was increased to 550° C. at a heating rate of 8° C. / min for 1 h to obtain a negative electrode material.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 is that the ethylenediamine in step S2 is replaced by butylamine.

[0072] Comparative Example 4

[0073] The difference between this comparative example and Example 1 is that the ethylenediamine in step S2 is replaced with triethylamine.

[0074] Comparative Example 5

[0075] This comparative example provides a method for preparing a negative electrode material, comprising the following steps:

[0076] S1: Under nitrogen atmosphere, mix 1 g of white phosphorus and 35 g of epoxy resin, dissolve in 80 mL of carbon disulfide solvent, and stir to obtain a mixed solution;

[0077] S2: The mixed solution was placed in a beaker and heated in a 50°C water bath for 120 min to remove carbon disulfide to obtain a mixture;

[0078] S3: placing the mixture in a sealed pressure reactor, heating it to 550°C at a heating rate of 8°C / min and reacting it for 1 hour, so that the epoxy resin decomposes and carbonizes into hard carbon to obtain a solid product;

[0079] S4: The solid product was crushed and passed through a 325-mesh sieve to obtain a negative electrode material.

[0080] Comparative Example 6

[0081] This comparative example provides a method for preparing a negative electrode material, comprising the following steps:

[0082] S1: Under nitrogen atmosphere, 1 g of white phosphorus, 35 g of epoxy resin, and 0.5 mL of catalyst ethylenediamine were mixed, dissolved in 80 mL of solvent carbon disulfide, and stirred to obtain a mixed solution;

[0083] S2: The mixed solution was placed in a beaker and heated in a 50°C water bath for 120 min to remove carbon disulfide to obtain a mixture;

[0084] S3: placing the mixture in a sealed pressure reactor, heating it to 550°C at a heating rate of 8°C / min and reacting it for 1 hour, so that the epoxy resin decomposes and carbonizes into hard carbon to obtain a solid product;

[0085] S4: The solid product was crushed and passed through a 325-mesh sieve to obtain a hard carbon-phosphorus composite negative electrode material.

[0086] Comparative Example 7

[0087] This comparative example provides a method for preparing a negative electrode material, comprising the following steps:

[0088] S1: Using epoxy resin as the carbon source, 36 g of epoxy resin was placed in a pressure reactor and heated to 550 °C at a heating rate of 8 °C / min for 1 h. The epoxy resin was decomposed and carbonized into hard carbon.

[0089] S2: Weigh 1 g of red phosphorus, mix it with hard carbon by ball milling, and pass it through a 325-mesh sieve to obtain a negative electrode material.

[0090] The negative electrode materials prepared in the above embodiments and comparative examples were used as the negative electrode active material, and were uniformly mixed with vinylidene fluoride (PVDF) (dissolved in N-methylpyrrolidone) and conductive carbon black in a mass ratio of 90:5:5. The mixture was coated into an electrode film, dried in a vacuum drying oven at 120°C for 12 hours, and then rolled and punched to obtain a hard carbon negative electrode sheet. A metal sodium sheet was used as the counter electrode, and 1 mol / L NaPF6 (EC-DEC = 1:1) was used as the electrolyte. The hard carbon negative electrode sheets obtained above were assembled into 2430 button-type batteries in a glove box, and their electrochemical performance was tested. The test data are shown in Table 1:

[0091] Table 1

[0092]

[0093] As can be seen from the data in the above table, the preparation methods provided in each embodiment of the present invention can obtain hard carbon-phosphorus composite negative electrode materials with better structures; the sodium ion batteries prepared using the hard carbon-phosphorus composite negative electrode materials provided in each embodiment have excellent long cycle life characteristics after testing.

[0094] The hard carbon material prepared in Comparative Example 1 using epoxy resin as a carbon source has a charge and discharge capacity significantly lower than that of Example 1.

[0095] In Comparative Example 2, the negative electrode material prepared directly using white phosphorus as the raw material has a high charge and discharge capacity, but the initial coulombic efficiency and capacity retention rate are significantly reduced.

[0096] The difference between Comparative Examples 3 and 4 and Example 1 is that butylamine and triethylamine are used to replace ethylenediamine to prepare the hard carbon material. After testing, the charge and discharge capacities of the two are reduced.

[0097] Compared with Example 1, in Comparative Example 5, no ethylenediamine was added during the preparation process, the resin was not completely cured, more pores were formed by carbonization, and the initial efficiency and cycle performance decreased.

[0098] Compared with Example 1, in Comparative Example 6, white phosphorus, epoxy resin, and ethylenediamine are directly mixed and then dissolved in a solvent during the preparation process. The resin solidifies before being mixed with the solvent, and phosphorus does not form a uniform nano-distribution, which affects the capacity of the material and reduces the initial efficiency and cycle performance.

[0099] Compared with Example 1, in Comparative Example 7, hard carbon was first prepared using epoxy resin as a carbon source, and then the prepared hard carbon was mixed with red phosphorus by ball milling to obtain a negative electrode material. The red phosphorus in this negative electrode material physically adhered to the surface of the hard carbon. The hard carbon could not effectively improve the volume expansion and contraction of the red phosphorus during charge and discharge, and the red phosphorus could not form a uniform nano-distribution, and there was local agglomeration. Therefore, the material capacity was lower than that of Example 1, and the initial efficiency and cycle performance were reduced.

[0100] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a hard carbon-phosphorus composite negative electrode material, characterized in that: The steps include: S1: Under an inert atmosphere, white phosphorus and a carbon source are mixed and dissolved in a solvent to obtain a mixed solution; S2: adding a catalyst to the mixed solution to obtain a reaction solution; S3: heating the reaction solution at 50° C. to obtain a mixture; S4: placing the mixture in a sealed pressure reactor, heating to 500-600° C. and reacting for 1 hour to obtain a solid product; S5: crushing the solid product to obtain a hard carbon-phosphorus composite negative electrode material with uniformly distributed nano red phosphorus particles.

2. The method for preparing a hard carbon-phosphorus composite negative electrode material according to claim 1, wherein: The catalyst is ethylenediamine.

3. The method for preparing a hard carbon-phosphorus composite negative electrode material according to claim 2, wherein: The carbon source is resin.

4. The method for preparing a hard carbon-phosphorus composite negative electrode material according to claim 3, wherein: The resin is selected from at least one of phenolic resin, epoxy resin and urea-formaldehyde resin.

5. The method for preparing a hard carbon-phosphorus composite negative electrode material according to claim 1, wherein: The solvent is carbon disulfide.

6. The method for preparing a hard carbon-phosphorus composite negative electrode material according to any one of claims 1 to 5, characterized in that: The usage ratio of the white phosphorus, the carbon source, the catalyst, and the solvent is 1 g: (20-50) g: (0.1-0.8) mL: (50-100) mL.

7. The method for preparing a hard carbon-phosphorus composite negative electrode material according to claim 6, wherein: The heating method in step S3 is water bath heating.

8. The method for preparing a hard carbon-phosphorus composite negative electrode material according to claim 6, wherein: The heating rate in step S4 is (5-10)°C / min.

9. A hard carbon-phosphorus composite negative electrode material, characterized in that: The hard carbon-phosphorus composite negative electrode material is prepared by the preparation method of any one of claims 1 to 8.

10. A sodium ion battery, characterized in that: Comprising the hard carbon-phosphorus composite negative electrode material as claimed in claim 9.

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