Phosphorus negative electrode material and preparation method thereof

Abstract

The application provides a phosphorus negative electrode material and a preparation method thereof, and belongs to the technical field of high specific energy batteries. The preparation method comprises the following steps: 1) preparing a first phosphorus / carbon composite material into an electrode, and testing the initial irreversible capacity of the electrode; 2) placing a second phosphorus / carbon composite material between at least two metal sodium foils, preparing an ultrathin Na / Na3P / C composite foil through repeated mechanical rolling and folding, and making the capacity generated by the obtained ultrathin Na / Na3P / C composite foil equivalent to the initial irreversible capacity of the electrode prepared from the first phosphorus / carbon composite material in step 1); and 3) directly covering the ultrathin Na / Na3P / C composite foil obtained in step 2) on the surface of the first phosphorus / carbon composite material to form a high reversible capacity phosphorus negative electrode material. The ultrathin Na / Na3P / C composite foil is simple in sodium compensation operation for the phosphorus negative electrode and has no side effects on residues, effectively overcomes the deficiencies of additive doping pre-sodium and metal sodium contact pre-sodium, and improves the capacity of a sodium ion battery, and further improves the energy density of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high specific energy batteries, and particularly relates to a phosphorus negative electrode material and a preparation method thereof. BACKGROUND

[0002] Currently, lithium ion batteries are widely used in battery products, electric vehicles and power grid storage and other fields and show great market prospects. Unfortunately, the shortage and uneven distribution of lithium resources hinder the large-scale application of lithium ions (such as power grid energy storage). Sodium resources are abundant, and the similar physicochemical properties of sodium and lithium enable the research and development of sodium ion batteries to adopt or draw on the technology of lithium ion batteries. Therefore, sodium ion batteries are widely considered as an important direction for the development of the next generation of electrochemical energy storage devices. However, due to the theoretical specific capacity of the hard carbon negative electrode being lower than 300 mAh g −1 Therefore, the current commercial sodium ion battery has an energy density lower than 150 Wh kg −1 , which is about half of that of lithium ion batteries, which greatly hinders its application. Therefore, the research of high specific capacity negative electrode materials is the key to the development of sodium ion batteries.

[0003] The theoretical specific capacity of the phosphorus negative electrode for sodium storage is the highest among all candidate materials, reaching 2596 mAh g −1 , which is an ideal choice for high specific energy sodium ion battery negative electrode materials. However, the huge volume change of phosphorus-based negative electrode materials during charging / discharging requires them to be made into nanostructures or be compounded with carbon materials with large specific surface area. Although the cycle stability is improved, the active sites they provide inevitably increase the irreversible loss of sodium during the initial cycle.

[0004] Therefore, how to improve the initial reversible specific capacity is crucial for the development of phosphorus negative electrodes and the improvement of the energy density of sodium ion batteries. Pre-sodiumization (sodium compensation) is a technology that preloads a sodium foil or a sodium-rich material on the surface of the electrode to compensate for the irreversible sodium loss during the initial cycle of the battery, which provides an effective solution to reduce the irreversible capacity loss in sodium ion batteries.

[0005] Pre-sodiumization technology can be divided into four categories: additive doping pre-sodiumization, electrochemical pre-sodiumization, chemical pre-sodiumization and metal sodium contact pre-lithiation. Among them,

[0006] After sodium compensation, additive doping pre-sodiumization will have some non-active substances remaining on the surface of the electrode, which will affect the performance of the battery. In addition, most of these pre-sodiumization materials have high activity and poor air stability.

[0007] Electrochemical pre-sodiumization usually requires the battery to be disassembled and assembled again, which requires complex equipment and harsh operating environment, thereby reducing the usability of this technology in commercial battery manufacturing.

[0008] The pre-sodiation agent used in chemical pre-sodiation is usually highly reactive, and the pre-sodiation operation needs to be carried out in an inert atmosphere. The electrode material after sodiation also has a certain reactivity, and the material is in a metastable state. In the subsequent slurry mixing and coating process, the electrode sheet is easy to absorb water or react with other additives, which is not conducive to battery processing.

[0009] The sodium foil contact pre-sodiation uses a metal sodium foil as a pre-sodiation agent. The excess sodium foil needs to be removed at the end of pre-sodiation, and it is difficult to accurately control the amount of sodium compensation. SUMMARY

[0010] The present application provides a kind of phosphorus negative electrode material and preparation method thereof, by adding a layer of thickness controllable ultra-thin sodium metal composite foil on the surface of original high capacity phosphorus / carbon composite electrode, i.e. using the pre-sodiation effect of ultra-thin sodium metal composite foil and high initial irreversible capacity phosphorus / carbon composite electrode to construct new phosphorus negative electrode material. The added composite foil acts as a pre-sodiation agent to compensate for the capacity loss caused by the initial irreversible reaction of the original phosphorus / carbon composite electrode (initial irreversible capacity). By controlling the thickness of the composite foil, the excess sodium foil does not need to be removed at the end of pre-sodiation, and the whole is a new phosphorus negative electrode material.

[0011] The present application provides a kind of phosphorus negative electrode material and preparation method thereof, by adding a layer of thickness controllable ultra-thin sodium metal composite foil on the surface of original high capacity phosphorus / carbon composite electrode, i.e. using the pre-sodiation effect of ultra-thin sodium metal composite foil and high initial irreversible capacity phosphorus / carbon composite electrode to construct new phosphorus negative electrode material. The added composite foil acts as a pre-sodiation agent to compensate for the capacity loss caused by the initial irreversible reaction of the original phosphorus / carbon composite electrode (initial irreversible capacity). By controlling the thickness of the composite foil, the excess sodium foil does not need to be removed at the end of pre-sodiation, and the whole is a new phosphorus negative electrode material.

[0012] 1) The first phosphorus / carbon composite material is prepared into an electrode, and the initial irreversible capacity of the electrode is tested;

[0013] 2) The second phosphorus / carbon composite material is placed between at least two layers of metal sodium foil, and an ultra-thin Na / Na3P / C composite foil is prepared by repeated mechanical rolling and folding, so that the capacity generated by the obtained ultra-thin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the electrode prepared from the first phosphorus / carbon composite material obtained in step 1);

[0014] 3) The ultra-thin Na / Na3P / C composite foil obtained in step 2) is directly covered on the surface of the first phosphorus / carbon composite material to form a high reversible capacity phosphorus negative electrode material.

[0015] Further, in step 2), the addition amount of the second phosphorus / carbon composite material accounts for 5-25% of the total mass of the ultra-thin Na / Na3P / C composite foil.

[0016] Further, in step 2), the addition amount of the second phosphorus / carbon composite material accounts for 15% of the total mass of the ultra-thin Na / Na3P / C composite foil.

[0017] Further, in step 2), the specific thickness of the ultra-thin Na / Na3P / C composite foil is 5-30 μm.

[0018] Furthermore, in step 2), the specific thickness of the ultra-thin Na / Na3P / C composite foil is 15 μm.

[0019] Furthermore, the phosphorus in the first phosphorus / carbon composite material or the second phosphorus / carbon composite material includes at least one of red phosphorus, black phosphorus, yellow phosphorus, and purple phosphorus; and the carbon includes at least one of hard carbon, amorphous carbon, graphene sheets, redox graphene sheets, biomass carbon, and carbon nanotubes.

[0020] Furthermore, the mass content of carbon in the first phosphorus / carbon composite material is 1-50%.

[0021] Furthermore, the mass content of carbon in the second phosphorus / carbon composite material is 1-24%.

[0022] The present invention also proposes a phosphorus negative electrode material prepared by any of the above preparation methods.

[0023] The present invention has the following advantages:

[0024] The present invention uses an ultrathin Na / Na3P / C composite foil as a pre-sodiumization material for the phosphorus negative electrode. First, a second phosphorus / carbon composite material and a metallic sodium foil are repeatedly mechanically rolled and folded, wherein phosphorus reacts with metallic sodium to form Na3P. This enhances the machinability of sodium and produces a low-capacity ultrathin Na / Na3P / C composite foil. Then, the ultrathin Na / Na3P / C composite foil is used to perform sodium compensation on the first phosphorus / carbon composite material, i.e., the phosphorus negative electrode. The residue is a fast ion conductor, Na3P, and slightly sodiumized carbon, which not only does not affect the performance of the battery but also helps to improve the stability of the electrode interface. The simplicity of the ultrathin Na / Na3P / C composite foil for sodium compensation of the phosphorus negative electrode and the lack of side effects of the residue effectively overcome the shortcomings of additive doping pre-sodiumization and metallic sodium contact pre-sodiumization, and improve the capacity of the sodium ion battery, thereby improving the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 This is the XRD pattern of the phosphorus / carbon composite material obtained in Example 1 of the present invention.

[0027] Figure 2 This is the initial charge / discharge curve of the phosphorus / carbon negative electrode obtained in Example 1 of the present invention.

[0028] Figure 3 This is the XRD pattern of the Na / Na3P / C composite foil obtained in Example 1 of the present invention.

[0029] Figure 4Digital photo of Na / Na3P / C composite foil obtained in Example 1 of the present application and pure Na foil of Comparative Example 2.

[0030] Figure 5 Curve of complete removal of elemental sodium in Na / Na3P / C composite foil obtained in Example 1 of the present application.

[0031] Figure 6 Cycle diagram of Na / Na3P / C composite foil obtained in Test Example 1 of the present application for improving specific capacity of phosphorus / carbon negative electrode-based battery. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be apparently and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0033] The present application provides a preparation method of a phosphorus negative electrode material, comprising the following steps:

[0034] 1) An electrode is prepared from a first phosphorus / carbon composite material, and the initial irreversible capacity of the electrode is tested;

[0035] 2) A second phosphorus / carbon composite material is placed between at least two metal sodium foils, and an ultrathin Na / Na3P / C composite foil is prepared through repeated mechanical rolling and folding, so that the capacity generated by the obtained ultrathin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the electrode prepared from the first phosphorus / carbon composite material in step 1);

[0036] 3) The ultrathin Na / Na3P / C composite foil obtained in step 2) is directly covered on the surface of the first phosphorus / carbon composite material, to form a high-reversible-capacity phosphorus negative electrode material.

[0037] In the present application, the ultrathin Na / Na3P / C composite foil is used as a pre-sodiumized material of the phosphorus negative electrode. First, the second phosphorus / carbon composite material is repeatedly mechanically rolled and folded with the metal sodium foil, in which the phosphorus reacts with the metal sodium to generate Na3P, so as to enhance the mechanical processability of sodium and prepare an ultrathin Na / Na3P / C composite foil with low capacity. Then, the ultrathin Na / Na3P / C composite foil is used for sodium compensation of the first phosphorus / carbon composite material, i.e., the phosphorus negative electrode, and the residues are fast ionic conductor Na3P and slightly sodiumized carbon, which not only do not affect the performance of the battery, but also help to improve the stability of the electrode interface. The simplicity of the operation of the ultrathin Na / Na3P / C composite foil for sodium compensation of the phosphorus negative electrode and the non-side effects of the residues effectively overcome the deficiencies of the additive-doped pre-sodiumization and the metal sodium contact pre-sodiumization, and improve the capacity of the sodium ion battery, and further improve the energy density of the battery.

[0038] In step 1) of the embodiment of the present application, the initial irreversible capacity of the first phosphorus / carbon composite material after being prepared into an electrode is tested to clearly determine the amount of capacity to be compensated subsequently.

[0039] In step 2) of the embodiment of the present application, mechanical rolling causes the interface reaction of phosphorus and sodium to form a fast ion conductor Na3P. With the increase of the number of rolling, the phosphorus is completely converted into Na3P and uniformly embedded in the Na block, thereby obtaining the Na / Na3P / C composite foil. Na3P is uniformly distributed in the composite foil, and thus the amount of the second phosphorus / carbon composite material added has an important influence on the capacity of the composite foil, and the thickness of the composite foil is also proportional to the capacity.

[0040] In an embodiment of the present application, in step 2), the content of Na3P and C in the Na / Na3P / C composite foil directly affects whether it can be prepared into an ultrathin composite foil by mechanical rolling. Therefore, in order to ensure that the composite foil with the required thickness is obtained, the amount of the second phosphorus / carbon composite material added accounts for 5-25% of the total mass of the ultrathin Na / Na3P / C composite foil. Preferably, in step 2), the amount of the second phosphorus / carbon composite material added accounts for 15% of the total mass of the ultrathin Na / Na3P / C composite foil. In the embodiment of the present application, the amount of the second phosphorus / carbon composite material added has a certain influence on the capacity of the Na / Na3P / C composite foil. Too high amount of the second phosphorus / carbon composite material added will cause the sodium metal to be completely reacted and unable to form a foil, and too low amount of the second phosphorus / carbon composite material added will cause the sodium metal to be almost not reacted and unable to be thinned, so an appropriate amount of the second phosphorus / carbon composite material needs to be added.

[0041] In an embodiment of the present application, in step 2), the specific thickness of the ultrathin Na / Na3P / C composite foil is 5-30 μm; preferably, the specific thickness of the ultrathin Na / Na3P / C composite foil is 15 μm. The thickness of the ultrathin Na / Na3P / C composite foil has a certain influence on the composite foil. Too thick Na / Na3P / C composite foil will cause excessive active sodium, and too thin Na / Na3P / C composite foil will cause insufficient active sodium.

[0042] Specifically, in steps 1) and 2), the first phosphorus / carbon composite material and the second phosphorus / carbon composite material are prepared by a ball milling method or a chemical method. The phosphorus in the first phosphorus / carbon composite material or the second phosphorus / carbon composite material includes at least one of red phosphorus, black phosphorus, yellow phosphorus, and purple phosphorus; and the carbon includes at least one of hard carbon, amorphous carbon, graphene sheet, redox graphene sheet, biomass carbon, and carbon nanotube. The mass content of the carbon in the first phosphorus / carbon composite material is 1-50%, and the mass content of the carbon in the second phosphorus / carbon composite material is 1-24%.

[0043] The embodiment of the present application also provides a phosphorus negative electrode material prepared by the preparation method.

[0044] The phosphorus negative electrode material provided by the embodiment of the present application uses a new electrode of ultra-thin Na / Na3P / C composite foil and high-capacity phosphorus / carbon negative electrode, which can effectively improve the energy density of the battery without side effects.

[0045] The present application will be described in detail below with reference to the embodiments and drawings.

[0046] Example 1 A preparation method of a phosphorus negative electrode material includes the following steps:

[0047] A first phosphorus / carbon composite material with a carbon mass content of 50% is prepared into an electrode, and its initial irreversible capacity loss is evaluated by charging / discharging;

[0048] A second phosphorus / carbon composite material with a carbon mass content of 20% is prepared into an ultra-thin Na / Na3P / C composite foil (about 20 μm) by repeatedly mechanically rolling and folding the second phosphorus / carbon composite material and sodium according to a mass ratio of 15:85, so that the capacity generated by the ultra-thin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity (initial sodium loss) of the first red phosphorus / carbon composite material.

[0049] The ultra-thin Na / Na3P / C composite foil is covered on the surface of the electrode prepared from the first phosphorus / carbon composite material, and a new phosphorus / carbon composite negative electrode is obtained.

[0050] Figure 1 The XRD pattern of the obtained phosphorus / carbon composite material is shown in FIG. 1. Figure 1 It can be seen that the phosphorus in the phosphorus / carbon composite material is in an amorphous structure.

[0051] Figure 2 The initial charging / discharging curve of the phosphorus / carbon negative electrode is shown in FIG. 2. Figure 2 It can be seen that the initial coulombic efficiency of the phosphorus / carbon composite electrode is 67.9%, that is, the initial irreversible capacity loss is 32.1%.

[0052] Figure 3 The XRD pattern of the Na / Na3P / C composite foil is shown in FIG. 3. Figure 3 It can be seen that the phosphorus in the second phosphorus / carbon composite material is completely converted into Na3P, and the Na / Na3P / C composite foil is composed of Na, Na3P and C.

[0053] Figure 4 (a) is a digital photo of the Na / Na3P / C composite foil. As shown in (a), Figure 4 It can be seen from (a) that the 20 μm thick and complete Na / Na3P / C composite foil is successfully prepared.

[0054] Example 2 A preparation method of a phosphorus negative electrode material includes the following steps:

[0055] A first red phosphorus / carbon composite material containing 50% carbon is prepared into an electrode, and its initial irreversible capacity loss is evaluated by charge / discharge;

[0056] A second red phosphorus / carbon composite material containing 1% carbon is mixed with metallic sodium at a mass ratio of 15:85, and repeated mechanical rolling and folding is performed to convert the phosphorus into Na3P particles completely, so as to prepare an ultrathin Na / Na3P / C composite foil (about 25 μm), so that the capacity generated by the ultrathin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the first red phosphorus / carbon composite material;

[0057] The ultrathin Na / Na3P / C composite foil is covered on the surface of the electrode prepared from the first red phosphorus / carbon composite material, so as to obtain a modified phosphorus / carbon composite negative electrode.

[0058] Example 3 A preparation method of a phosphorus negative electrode material, comprising the following steps:

[0059] A first red phosphorus / carbon composite material containing 50% carbon is prepared into an electrode, and its initial irreversible capacity loss is evaluated by charge / discharge;

[0060] A second red phosphorus / carbon composite material containing 24% carbon is mixed with metallic sodium at a mass ratio of 15:85, and repeated mechanical rolling and folding is performed to convert the phosphorus into Na3P particles completely, so as to prepare an ultrathin Na / Na3P / C composite foil (about 5 μm), so that the capacity generated by the ultrathin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the first red phosphorus / carbon composite material;

[0061] The ultrathin Na / Na3P / C composite foil is covered on the surface of the electrode prepared from the first red phosphorus / carbon composite material, so as to obtain a modified phosphorus / carbon composite negative electrode.

[0062] Example 4 A preparation method of a phosphorus negative electrode material, comprising the following steps:

[0063] A first red phosphorus / carbon composite material containing 10% carbon is prepared into an electrode, and its initial irreversible capacity loss is evaluated by charge / discharge;

[0064] A second red phosphorus / carbon composite material containing 24% carbon is mixed with metallic sodium at a mass ratio of 15:85, and repeated mechanical rolling and folding is performed to convert the phosphorus into Na3P particles completely, so as to prepare an ultrathin Na / Na3P / C composite foil (about 10 μm), so that the capacity generated by the ultrathin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the first red phosphorus / carbon composite material;

[0065] The ultra-thin Na / Na3P / C composite foil is covered on the surface of the electrode prepared from the first red phosphorus / carbon composite material to obtain a modified phosphorus / carbon composite negative electrode.

[0066] Example 5 A preparation method of a phosphorus negative electrode material includes the following steps:

[0067] A first red phosphorus / carbon composite material containing 10% of carbon is prepared into an electrode, and the initial irreversible capacity thereof is evaluated through charging / discharging;

[0068] A second red phosphorus / carbon composite material containing 1% of carbon is prepared into an ultra-thin Na / Na3P / C composite foil (about 15 μm) by repeatedly mechanically rolling and folding the second red phosphorus / carbon composite material and sodium according to a mass ratio of 15:85, so that the capacity generated by the ultra-thin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the first red phosphorus / carbon composite material;

[0069] The ultra-thin Na / Na3P / C composite foil is covered on the surface of the electrode prepared from the first red phosphorus / carbon composite material to obtain a modified phosphorus / carbon composite negative electrode.

[0070] Example 6 A preparation method of a phosphorus negative electrode material includes the following steps:

[0071] A first red phosphorus / carbon composite material containing 50% of carbon is prepared into an electrode, and the initial irreversible capacity thereof is evaluated through charging / discharging;

[0072] A second red phosphorus / carbon composite material containing 10% of carbon is prepared into an ultra-thin Na / Na3P / C composite foil (about 30 μm) by repeatedly mechanically rolling and folding the second red phosphorus / carbon composite material and sodium according to a mass ratio of 5:95, so that the capacity generated by the ultra-thin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the first red phosphorus / carbon composite material;

[0073] The ultra-thin Na / Na3P / C composite foil is covered on the surface of the electrode prepared from the first red phosphorus / carbon composite material to obtain a modified phosphorus / carbon composite negative electrode.

[0074] Example 7 A preparation method of a phosphorus negative electrode material includes the following steps:

[0075] A first red phosphorus / carbon composite material containing 50% of carbon is prepared into an electrode, and the initial irreversible capacity thereof is evaluated through charging / discharging;

[0076] A second red phosphorus / carbon composite material with a carbon content of 10% and metallic sodium in a mass ratio of 25:75 were repeatedly mechanically rolled and folded to completely convert the phosphorus into Na3P particles, thereby preparing an ultrathin Na / Na3P / C composite foil (approximately 12 μm). The capacity of the ultrathin Na / Na3P / C composite foil was comparable to the initial irreversible capacity of the first red phosphorus / carbon composite material.

[0077] An ultra-thin Na / Na3P / C composite foil is covered on the surface of an electrode prepared from the first red phosphorus / carbon composite material to obtain a modified phosphorus / carbon composite negative electrode.

[0078] Comparative Example 1 A method for preparing a phosphorus negative electrode material comprises the following steps:

[0079] The first red phosphorus / carbon composite material containing 50% carbon is prepared into an electrode.

[0080] Comparative Example 2 A method for preparing a phosphorus negative electrode material comprises the following steps:

[0081] Metallic sodium is placed on the surface of the first phosphorus / carbon composite material. Since metallic sodium cannot be compressed thinly, it cannot be directly pressed onto the surface of the first phosphorus / carbon composite material.

[0082] Figure 4 (b) is a digital photo of pure Na foil. Figure 4 It can be seen that the 20 μm thick and complete Na / Na3P / C composite foil was successfully prepared in Example 1. However, the pure sodium foil adhered to the plastic bag after being rolled to 50 μm and could not be removed completely.

[0083] Test Example 1

[0084] (1) The Na / Na3P / C composite foil and metallic sodium obtained in Example 1 were used as electrodes to assemble a battery, so that the active sodium in the Na / Na3P / C composite foil was completely removed, and the content of active sodium in the Na / Na3P / C composite foil was determined. Figure 5 .Depend on Figure 5 The capacity of Na / Na3P / C composite foil is about 625 mAh g −1 The 20μm Na / Na3P / C composite foil has a capacity of approximately 1.2 mAh.

[0085] (2) The phosphorus / carbon composite negative electrode obtained in Example 1 and the phosphorus / carbon composite electrode obtained in Comparative Example 1 were respectively matched with a sodium nickel iron manganese oxide positive electrode to assemble a full battery, and the charge / discharge cycle was carried out at a current density of 0.1 / 0.5C to test the electrochemical performance of the battery. Figure 6 . Figure 6A cycle plot of the Na / Na3P / C composite foil obtained from Example 1 to improve the specific capacity of the phosphorus / carbon negative electrode-based battery. The battery was assembled from Figure 6 It can be seen that the capacity of the battery assembled from the new phosphorus / carbon composite material formed by the Na / Na3P / C composite foil and the most original first red phosphorus / carbon composite material in Comparative Example 1 has been significantly improved compared with the most original first red phosphorus / carbon composite material.

[0086] The above merely provides the preferred embodiments of the present application, but is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a phosphorus negative electrode material, characterized in that: The steps include: 1) preparing the first phosphorus / carbon composite material into an electrode, and testing the initial irreversible capacity of the electrode; 2) placing the second phosphorus / carbon composite material between at least two layers of sodium metal foil, and preparing an ultrathin Na / Na3P / C composite foil by repeated mechanical rolling and folding, so that the capacity of the obtained ultrathin Na / Na3P / C composite foil is equivalent to the initial irreversible capacity of the electrode prepared from the first phosphorus / carbon composite material obtained in step 1); 3) The ultra-thin Na / Na3P / C composite foil obtained in step 2) is directly covered on the surface of the first phosphorus / carbon composite material to form a high reversible capacity phosphorus negative electrode material.

2. The preparation method according to claim 1, characterized in that In step 2), the amount of the second phosphorus / carbon composite material added is 5-25% of the total mass of the ultra-thin Na / Na3P / C composite foil.

3. The preparation method according to claim 2, characterized in that In step 2), the amount of the second phosphorus / carbon composite material added accounts for 15% of the total mass of the ultra-thin Na / Na3P / C composite foil.

4. The preparation method according to claim 1, characterized in that In step 2), the specific thickness of the ultra-thin Na / Na3P / C composite foil is 5-30 μm.

5. The preparation method according to claim 4, characterized in that In step 2), the specific thickness of the ultra-thin Na / Na3P / C composite foil is 15 μm.

6. The preparation method according to claim 1, characterized in that The phosphorus in the first phosphorus / carbon composite material or the second phosphorus / carbon composite material includes at least one of red phosphorus, black phosphorus, yellow phosphorus, and purple phosphorus; and the carbon includes at least one of hard carbon, amorphous carbon, graphene sheets, redox graphene sheets, biomass carbon, and carbon nanotubes.

7. The preparation method according to claim 1, characterized in that The mass content of carbon in the first phosphorus / carbon composite material is 1-50%.

8. The preparation method according to claim 1, characterized in that The mass content of carbon in the second phosphorus / carbon composite material is 1-24%.

9. The phosphorus negative electrode material prepared by the preparation method according to any one of claims 1 to 8.

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