A phosphorus-silicon co-doped silicon-carbon composite negative electrode material and its preparation method

Abstract

The present invention relates to a preparation method of a phosphorus-silicon co-doped silicon-carbon composite negative electrode material, comprising the following steps: (S1) placing a porous carbon material in a fluidized bed, replacing the gas in the fluidized bed with an inert gas, introducing a phosphorus source gas under heating conditions, and performing chemical vapor deposition of phosphorus; the ratio of the volume of the phosphorus source gas introduced to the mass of the porous carbon is 10-20 L:1 kg; (S2) then introducing a mixed gas of a phosphorus source gas and a silicon source gas, wherein the proportion of the phosphorus source gas in the mixed gas continuously decreases, and the ratio of the volume of the phosphorus source gas introduced to the volume of the silicon source gas introduced to the mass of the porous carbon is 120-170 L:420-600 L:1 kg; (S3) finally introducing a hydrocarbon gas for carbon coating. The prepared silicon-carbon composite negative electrode material has layered incorporation of phosphorus and silicon elements in the inner shell, which is beneficial to solving the problem of poor lithium ion transport kinetics in the silicon-carbon interface layer, and can reduce the volume expansion and stress release of silicon during lithium insertion and extraction, thereby improving the rate performance and long cycle performance of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a phosphorus-silicon co-doped silicon-carbon composite negative electrode material and a preparation method thereof. Background Art

[0002] In recent years, silicon-carbon composite negative electrode materials with high specific capacity have gradually been developed and have become an important research direction for improving the energy density of lithium-ion batteries. Silicon-based negative electrodes are accompanied by severe volume expansion during the process of lithium insertion and extraction, resulting in poor battery cycle life and limiting their commercial application.

[0003] Using porous carbon as a framework and depositing nanosilicon within the pores of the porous carbon can effectively slow silicon's volume expansion. However, silicon's poor conductivity further affects the material's rate performance. The introduction of phosphorus can significantly enhance the material's kinetic properties, thereby improving the battery's rate and cycling performance. Numerous applications of phosphorus-nitrogen co-doped or boron-silicon co-doped composite materials in lithium-ion battery anodes have been reported.

[0004] CN118039835A discloses a method for preparing a gas-phase doped nitrogen and phosphorus silicon-carbon material, comprising the following steps: S11 taking an appropriate amount of decane and adding it to a beaker containing inorganic hydrofluoric acid, stirring continuously until it dissolves; S12 then performing electrolysis at a certain voltage, and after the reaction is completed, obtaining a fluorocarbon surfactant; step (2) preparation of a silicon-carbon precursor; S21 taking an appropriate amount of nano-silicon powder, uniformly dispersing it in a mixed solvent containing hydrofluoric acid, deionized water and ethanol, stirring for a period of time, filtering and drying to obtain surface pretreated nano-silicon powder; S22 then continuing to add an appropriate amount of nano-graphite powder to the nano-silicon powder and placing it in a chemical reactor; In a chemical deposition furnace, add an appropriate amount of fluorocarbon surfactant, set appropriate parameters, select nickel as a catalyst and perform chemical vapor deposition in an argon atmosphere to obtain a silicon-carbon precursor; step (3) preparation of gas-phase doped nitrogen and phosphorus silicon-carbon material: S31 take an appropriate amount of silicon-carbon precursor and mix it with an appropriate amount of doping reaction catalyst Ni(CO)4 to obtain a mixed system, and dry it for a period of time; S32 put the mixed system in a high-temperature furnace, under a certain temperature and atmosphere, introduce an appropriate amount of ammonia and phosphine to dope the silicon-carbon precursor with nitrogen and phosphorus; S33 after doping, wash the material and dry it for a period of time to obtain a nitrogen and phosphorus silicon-carbon material.

[0005] CN108172775A discloses a phosphorus-doped silicon-carbon negative electrode material for lithium-ion batteries. The material is prepared by spray-granulating a phosphorus-doped nano-silicon material with graphite and an organic carbon source and then sintering the material. The preparation method comprises the following steps: S1, uniformly dispersing the nano-silicon material in a phosphoric acid solution, then spray-granulating the material, and performing a primary sintering to obtain the phosphorus-doped nano-silicon material; S2, uniformly dispersing the phosphorus-doped nano-silicon material in water, adding graphite and an organic carbon source, spray-granulating the material after complete dispersion, and then performing a secondary sintering to obtain the phosphorus-doped silicon-carbon negative electrode material for lithium-ion batteries.

[0006] CN116895747A discloses a phosphorus-doped silicon-carbon composite material comprising an inner core and an outer layer, wherein the inner core comprises phosphorus-doped nano-silicon particles and a carbon skeleton having a porous structure, wherein at least a portion of the porous structure is filled with the phosphorus-doped nano-silicon particles, and the outer layer comprises a carbon coating. The preparation method comprises the following steps: (I) placing the carbon skeleton having a porous structure in a vapor deposition reactor, introducing a protective gas into the vapor deposition reactor while maintaining stirring and heating, introducing a gaseous phosphorus source and a gaseous silicon source into the vapor deposition reactor to undergo a vapor deposition reaction with the carbon skeleton to obtain composite particles, wherein at least a portion of the porous structure is filled with the gaseous silicon source and the gaseous phosphorus source; and (II) carbon coating the composite particles.

[0007] CN114156457A discloses a method for preparing a silicon-based material coated with nitrogen-phosphorus co-doped porous carbon, comprising the following steps: S1: dissolving a certain mass fraction of phytic acid in deionized water, adding a corresponding mass fraction of silicon-based material while continuously stirring on a heatable magnetic stirrer, heating at 70-90°C and continuing to stir until the solution becomes viscous, and then transferring the dried material to an oven at 80-90°C for further drying; S2: transferring the dried material to a tube furnace and heating it to the first stage under an inert atmosphere. temperature, 600~800℃ for 2~5h; continue to heat to the second temperature, 850~1000℃ for 1~2h, and naturally cool to room temperature to obtain the material; S3: mix the material obtained in S2 with guanidine hydrochloride to make the mass fraction of phytic acid 2%~5%, the mass fraction of guanidine hydrochloride 1%~5%, and the mass fraction of silicon-based material 90%~97%, calcined under an inert gas atmosphere, and naturally cooled to room temperature to obtain a nitrogen-phosphorus co-doped porous carbon-coated silicon-based material.

[0008] CN117613225A discloses a method for preparing a boron-doped silicon-carbon negative electrode material, comprising the following steps: A. removing contaminants on the surface of the carbon-based material using an RCA standard cleaning method, followed by repeated rinsing with anhydrous ethanol, then soaking in a hydrofluoric acid aqueous solution to remove the natural oxide layer on the surface, and finally vacuum drying; B. transferring the dried carbon-based material to a PECVD preparation chamber, evacuating the chamber, using silane, borane, and hydrogen as reaction gases to cause primary and secondary reactions for deposition, and cooling after deposition to obtain coated particles; wherein, The primary reaction is that silane and borane are impacted by electrons to produce ions and neutral groups, and the secondary reaction is that the ions and groups collide to form new groups; during the deposition process, the silane flow rate is controlled to be 6-10 sccm, the borane flow rate is 0.7-1.2 sccm, and the hydrogen flow rate is 160-200 sccm; C, the coated particles obtained in step B and the alcohol-soluble carbon source are fully dispersed and mixed in an organic solvent, and then vacuum dried to obtain a uniform mixture; D, the uniform mixture obtained in step C is calcined at a high temperature in an inert atmosphere, and after cooling, a boron-doped silicon-carbon negative electrode material is obtained.

[0009] CN117199298A discloses a method for preparing a boron-doped porous silicon-carbon composite material, comprising the following steps: step (1): fully mixing silicon material and boride in a certain proportion, and calcining the mixture at a high temperature in an argon atmosphere, wherein the high-temperature calcination temperature is 300-1200°C, the heating temperature is 2-10°C / min, and the holding time is 0.1-12h; the boride is at least one of boron oxide and boric acid; step (2): pickling the product obtained in step (1) with HF solution, washing and drying to obtain boron-doped porous silicon; step (3): depositing hydrocarbon gas on the surface of the boron-doped porous silicon by a CVD method to obtain a boron-doped porous silicon-carbon composite material.

[0010] CN114899398A discloses a preparation method for a boron-nitrogen co-doped carbon nanotube-coated silicon oxide composite material, comprising the following steps: (1) preparation of a precursor: dissolving urea, boric acid, polyethylene glycol and stannous chloride in an organic solvent and / or deionized water and stirring to obtain a mixed solution; adding silicon oxide powder to the mixed solution; and obtaining a carbonized precursor after ultrasonication, stirring and drying; and (2) carbonization of the precursor: pyrolyzing the carbonized precursor under an inert atmosphere and then cooling to obtain a boron-nitrogen co-doped carbon nanotube-coated silicon oxide composite material.

[0011] It can be seen that a lot of research has been done on doping silicon-carbon composite materials in the prior art to improve their electrochemical performance. The methods can be divided into solid-phase, liquid-phase mixed calcination method or vapor deposition method according to the doping mode of the doping source. The solid-phase and liquid-phase methods have the defect of poor uniformity due to element doping. Therefore, the vapor deposition method is more industrially significant at present. Nano-silicon is deposited in porous carbon using chemical vapor deposition, and non-electrochemically active SiC is generated at the silicon-carbon interface, which will hinder the kinetic transport of lithium ions and make the rate performance of the material poor. Phosphorus doping can effectively improve the rate performance of the material. The vapor deposition method in the above-mentioned prior art cannot fully exert the effect of phosphorus doping. Summary of the Invention

[0012] The purpose of the present invention is to solve the problem that the existing silicon-carbon composite materials have poor lithium ion kinetic transport performance due to the presence of non-electrochemically active silicon carbide at the silicon-carbon interface, which cannot meet the market demand for high rate performance and long cycle performance. The present invention proposes a method for preparing a phosphorus-boron co-doped silicon-carbon composite negative electrode material to improve the rate performance and cycle performance of lithium ion battery negative electrode materials. The present invention first chemically vapor deposits a layer of nano-phosphorus particles in the pores of porous carbon. The phosphorus attached to the porous carbon pores can form a carbon-phosphorus bond with carbon. The carbon-phosphorus bond has a stronger ability to conduct lithium ions than the silicon-carbon bond, which is beneficial to improving the lithium ion kinetic transport performance at the interface. Subsequently, the strategy of phosphorus-silicon co-deposition is adopted to simultaneously deposit phosphorus and silicon on the nano-phosphorus particle layer or on the porous carbon pores. In addition, during the phosphorus-silicon co-deposition process, the amount of phosphorus deposited decreases gradually. On the one hand, the incorporation of phosphorus can significantly improve the material's conductivity, thereby improving the material's rate performance. On the other hand, the atomic radius of phosphorus (0.106nm) is smaller than that of silicon (0.111nm). Phosphorus doping reduces the silicon unit cell. As the amount of phosphorus doped increases, the energy barrier that lithium ions need to overcome to embed into silicon increases, which helps reduce the material's expansion and improves its cycling performance. During the phosphorus-silicon co-deposition process, the proportion of phosphorus gradually decreases. At the junction with the first layer of nanophosphorus, the proportion of phosphorus in the phosphorus-silicon co-deposition is relatively high. The rapid transport of lithium ions at this interface layer can be achieved with the help of phosphorus. As the co-deposition time increases, the proportion of phosphorus gradually decreases at the intersection of the first nanophosphorus layer, while the proportion of silicon gradually increases. Therefore, during the process of lithium ion embedding from the outside to the inside, the presence of phosphorus is conducive to the rapid transport of lithium ions and reduces the expansion of silicon.

[0013] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0014] A method for preparing a phosphorus-silicon co-doped silicon-carbon composite negative electrode material comprises the following steps:

[0015] (S1) The porous carbon material is placed in a fluidized bed, the gas in the fluidized bed is replaced with an inert gas, and a phosphorus source gas is introduced under heating conditions to perform chemical vapor deposition of phosphorus; the ratio of the volume of the phosphorus source gas introduced to the mass of the porous carbon is 10-20 L: 1 kg;

[0016] (S2) Then, a mixture of phosphorus source gas and silicon source gas is introduced, and the proportion of phosphorus source gas in the mixed gas continues to decrease, and the ratio of the volume of phosphorus source gas introduced, the volume of silicon source gas introduced, and the mass of porous carbon is satisfied to be 120-170 L:420-600 L:1 kg.

[0017] (S3) Finally, hydrocarbon gas is introduced for carbon coating to prepare a phosphorus-silicon co-doped silicon-carbon composite negative electrode material.

[0018] Furthermore, in step (S1), the specific surface area of ​​the porous carbon is 1400-2200m 2 / g, pore volume of 0.7-1.2cm 3 / g, the micropore ratio is 70-98%, and the porous carbon particle size is 5-20μm; one of the inert gases is nitrogen, argon, and helium.

[0019] Furthermore, in steps (S1) and (S2), the phosphorus source gas is phosphorus hydride, or a phosphorus-containing gas generated by heating a solid phosphorus source, and the solid phosphorus source is selected from at least one of black phosphorus, white phosphorus, phosphorus pentoxide, phosphate, hydrogen phosphate, dihydrogen phosphate, metaphosphate, and alkyl phosphate.

[0020] Furthermore, in step (S2), the silane gas is selected from at least one of monosilane, disilane, dimethylsilane, dichlorodihydrosilane, and trichlorosilane.

[0021] Furthermore, in step (S1), the heating condition is 500-700°C, the flow rate of the phosphorus source gas is 0.1-0.3 L / min, and the introduction time satisfies the above-mentioned ratio of the volume of the phosphorus source gas introduced to the mass of the porous carbon.

[0022] Furthermore, in step (S2), the phosphorus source gas flow rate gradually decreases from 1-2 L / min to 0-0.1 L / min, the silicon source gas flow rate is 1-5 L / min, and the ratio of the phosphorus source gas input volume, the silicon source gas input volume and the porous carbon mass meets the above ratio.

[0023] Furthermore, in step (S3), the hydrocarbon gas is selected from at least one of methane, ethane, propane, ethylene, propylene, and acetylene. The amount of hydrocarbon gas introduced is such that the thickness of the carbon coating layer is 2-20 nm, preferably 5-10 nm, or the ratio of the hydrocarbon gas introduced to the porous carbon mass is 150-200 L:1 kg.

[0024] Compared with the prior art, the phosphorus-silicon co-doped silicon-carbon composite material provided by the present invention realizes the co-deposition of phosphorus and silicon in the porous carbon pores through a segmented chemical vapor deposition method, and in step (S1), a nano-phosphorus particle layer is introduced into the porous carbon pores, and the phosphorus attached to the porous carbon pores can form a carbon-phosphorus bond with the carbon. The carbon-phosphorus bond has a stronger ability to conduct lithium ions than the silicon-carbon bond, which is beneficial to improving the lithium ion kinetic transport performance at the interface. In addition, in step (S2), the phosphorus doping concentration is gradually reduced through phosphorus-silicon co-deposition. The introduction of phosphorus greatly improves the electrical conductivity of the material. The gradient difference in phosphorus doping concentration is beneficial to improving the rapid conduction of lithium ions inside the silicon crystal phase and realizing rapid conduction of lithium ions at the phosphorus-carbon interface, thereby achieving high rate performance and long cycle performance of the silicon-carbon composite negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The SEM image and element distribution diagram of the phosphorus-silicon co-deposited silicon-carbon composite anode material prepared in Example 1, the SEM image (a), Si element distribution image (b), C element distribution image (c), and P element distribution image (d) of a silicon-carbon composite anode material prepared by co-depositing silicon and boron elements on a porous carbon substrate and then carbon coating are provided;

[0026] Figure 2 This is the XRD pattern of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material of Example 1;

[0027] Figure 3 This is a charge and discharge curve diagram of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material of Example 1;

[0028] Figure 4 This is a scanning electron microscope image of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material of Example 1. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0030] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0031] Example 1

[0032] (S1) 500 g of porous carbon was added to a fluidized bed. At room temperature, the gas in the fluidized bed was converted to an oxygen content of ≤10 ppm using nitrogen. The temperature of the fluidized bed was raised to 600 °C and kept warm for 1 h. Then, phosphine gas was introduced under nitrogen protection at a nitrogen gas flow rate of 0.5 L / min, and the phosphine gas flow rate was controlled to 0.15 L / min. The phosphine ventilation time was 50 min.

[0033] (S2) Phosphine and monosilane gases are then introduced into the fluidized bed simultaneously, with the monosilane gas flow rate controlled at 2 L / min and the phosphine gas flow rate decreasing from 1 L / min to 0 L / min. After chemical vapor deposition for 140 min, the introduction of monosilane gas and phosphine gas is stopped. At this time, a total of 280 L of monosilane gas and 65.5 L of phosphine gas have been introduced into the fluidized bed.

[0034] (S3) While maintaining continuous nitrogen flow through the fluidized bed, the fluidized bed temperature was raised to 700°C. After holding the fluidized bed temperature for 1 hour, acetylene gas was introduced at a flow rate of 0.5 L / min for 3 hours to perform vapor phase coating. This yielded a carbon-coated silicon-carbon composite anode material in which phosphorus and silicon were co-deposited within the pores of the porous carbon.

[0035] Figure 1 These are the SEM images and element distribution diagrams of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material prepared in Example 1, which are SEM photo (a), Si element distribution diagram (b), C element distribution diagram (c) and P element distribution diagram (d).

[0036] Figure 2 This is the XRD diagram of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material of Example 1.

[0037] Figure 3 This is the charge and discharge curve of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material of Example 1.

[0038] Figure 4 This is a scanning electron microscope image of the phosphorus-silicon co-deposited silicon-carbon composite negative electrode material of Example 1.

[0039] Example 2

[0040] The same operation as in Example 1 was performed, except that in step (S2), the phosphine gas flow rate was decreased from 1.4 L / min to 0.1 L / min, and the total amount of phosphine gas introduced was controlled to be 85 L.

[0041] Example 3

[0042] The same operation as in Example 1 was performed, except that in step (S2), the flow rate of monosilane gas was controlled to 1.5 L / min.

[0043] Example 4

[0044] The same operation as in Example 1 was performed, except that in step (S2), the flow rate of monosilane gas was controlled to 2.14 L / min.

[0045] Example 5

[0046] The same operation as in Example 1 was performed, except that in step (S1), the phosphine gas flow rate was controlled to 0.3 L / min, and the phosphine ventilation time was 30 min.

[0047] Example 6

[0048] The same operation as in Example 1 was performed, except that in step (S1), the phosphine gas flow rate was controlled to 0.5 L / min, and the phosphine ventilation time was 15 min.

[0049] Comparative Example 1

[0050] (S1) adding 500 g of porous carbon to a fluidized bed, converting the gas in the fluidized bed to an oxygen content of ≤10 ppm with nitrogen at room temperature, raising the temperature of the fluidized bed to 600° C. and holding it for 1 h, then introducing phosphine gas under nitrogen protection at a nitrogen gas flow rate of 0.5 L / min and a phosphine gas flow rate of 1 L / min, with the phosphine ventilation time being 73 min;

[0051] (S2) Then, monosilane gas is simultaneously introduced into the fluidized bed at a flow rate of 2 L / min. After chemical vapor deposition for 140 min, the monosilane gas is stopped.

[0052] (S3) While maintaining continuous nitrogen flow through the fluidized bed, the fluidized bed temperature was raised to 700°C. After holding the fluidized bed temperature for 1 hour, acetylene gas was introduced at a flow rate of 0.5 L / min for 3 hours to perform vapor phase coating. This yielded a carbon-coated silicon-carbon composite anode material in which phosphorus and silicon were co-deposited within the pores of the porous carbon.

[0053] The volume of phosphine and the amount of silane gas introduced in Comparative Example 1 were the same as those in Example 1, but the phosphorus source gas and the silicon source gas were introduced separately in Comparative Example 1.

[0054] Comparative Example 2

[0055] (S1) 500 g of porous carbon was added to a fluidized bed. At room temperature, nitrogen was used to convert the gas in the fluidized bed to an oxygen content of ≤10 ppm. The temperature of the fluidized bed was raised to 600 ° C and kept warm for 1 hour. Then, phosphine gas and silane gas were introduced simultaneously under nitrogen protection. The nitrogen gas flow rate was 0.5 L / min, the monosilane gas flow rate was controlled to 2 L / min, and the phosphine gas flow rate was decreased from 1.1 L / min to 0 L / min. After chemical vapor deposition was carried out together for 140 minutes, the introduction of monosilane gas and phosphine gas was stopped. At this time, 280 L of monosilane gas and 73 L of phosphine gas were introduced.

[0056] (S2) While maintaining continuous nitrogen flow through the fluidized bed, the fluidized bed temperature was raised to 700°C. After holding the fluidized bed temperature for 1 hour, acetylene gas was introduced at a flow rate of 0.5 L / min for 3 hours to perform vapor phase coating. This yielded a carbon-coated silicon-carbon composite anode material in which phosphorus and silicon were co-deposited within the pores of the porous carbon.

[0057] The volume of phosphine introduced in Comparative Example 2 and the amount of silane gas introduced were the same as those in Example 1, but the phosphorus source gas and the silicon source gas were introduced simultaneously in Comparative Example 2, and there was no step (S1) of introducing phosphine gas at a low flow rate to perform phosphorus deposition in the example.

[0058] Comparative Example 3

[0059] 500g of porous carbon was added to a fluidized bed. At room temperature, nitrogen was used to convert the gas in the fluidized bed to an oxygen content of ≤10ppm. The fluidized bed temperature was raised to 600°C and held for 1 hour. Then, monosilane gas was introduced simultaneously under nitrogen protection. The monosilane gas flow rate was controlled to 2L / min and the monosilane gas ventilation time was controlled to 140min. After that, the monosilane gas was stopped. Maintaining the continuous flow of nitrogen into the fluidized bed, the fluidized bed temperature was raised to 700°C. After holding for 1 hour, acetylene gas was introduced at a gas flow rate of 0.5L / min for vapor phase coating. The acetylene ventilation time was 3 hours to obtain a carbon-coated silicon-carbon composite negative electrode material with silicon deposited in the pores of the porous carbon.

[0060] Comparative Example 4

[0061] 500g of porous carbon was added to a fluidized bed. At room temperature, nitrogen was used to reduce the oxygen content in the fluidized bed to ≤10ppm. The bed temperature was then raised to 600°C and held for 1 hour. Phosphine gas was then introduced under nitrogen at a rate of 1 L / min for 140 minutes, after which the phosphine addition was stopped. Maintaining the continuous flow of nitrogen, the bed temperature was raised to 700°C and held for 1 hour. Acetylene gas was then introduced at a rate of 0.5 L / min for 3 hours for vapor-phase coating. This resulted in a carbon-coated silicon-carbon composite anode material with phosphorus deposited within the pores of the porous carbon.

[0062] Test Case

[0063] The negative electrode materials provided in the examples and comparative examples are assembled into a battery in the following steps:

[0064] 1. Pole sheet preparation: The negative electrode material, conductive agent (Super-P), and polyacrylic acid (PAA) binder are mixed in a mass ratio of 80:10:10 to prepare a slurry. After stirring and mixing, the slurry is coated on the copper foil current collector. After drying at room temperature, the slurry is placed in a vacuum oven and further dried at 60°C under vacuum conditions for 12 hours to obtain the pole sheet.

[0065] 2. Battery assembly: Cut the above-obtained electrode into a circular electrode with a diameter of 10 mm and an active material loading of 1.3

[0066] mg / cm2; metallic lithium sheet as the counter electrode, 1 mol / L LiPF6 (the solvent is a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, with 5% volume of fluoroethylene carbonate added) as the electrolyte, and polypropylene microporous membrane, were assembled into 2032-type button cells in an argon atmosphere glove box, with 50 μL of electrolyte added to each cell.

[0067] The assembled battery was charged and discharged on a LAND charge and discharge tester in the range of 50 mV to 1.5 V, with a compaction density of 1.1 g / cm 3 After three charge and discharge cycles at a current density of 0.1 C (1 C = 1500 mA / g), rate charge and discharge tests were performed at a current density of 2 C. The results are shown in Table 1 below.

[0068] Table 1 Electrical performance data

[0069] .

[0070] As can be seen from Table 1, the silicon-carbon composite negative electrode material prepared by chemical vapor co-deposition of silane gas and phosphine gas has excellent electrochemical properties, particularly rate capability and long cycle stability. In Comparative Example 1 and Comparative Example 2, the phosphine feeding amount and the silane gas feeding amount are the same as in Example 1, but in Comparative Example 1, the phosphorus source gas and the silicon source gas are fed respectively, while Comparative Example 2 is fed simultaneously, and there is no embodiment step (S1) in which the phosphine gas is first fed at a low flow rate to carry out the deposition of phosphorus. Although both are silicon-phosphorus co-doping, the function of dual doping cannot be effectively brought into play.

Claims

1. A method for preparing a phosphorus-silicon co-doped silicon-carbon composite negative electrode material, characterized in that: The following steps are involved: (S1) The porous carbon material is placed in a fluidized bed, the gas in the fluidized bed is replaced with an inert gas, and a phosphorus source gas is introduced under heating conditions to perform chemical vapor deposition of phosphorus; the ratio of the introduced phosphorus source gas volume to the porous carbon mass is 10-20 L:1 kg; the heating conditions are 500-700° C., and the phosphorus source gas flow rate is 0.1-0.3 L / min; (S2) Then, a mixture of phosphorus source gas and silicon source gas is introduced, wherein the proportion of phosphorus source gas in the mixed gas continuously decreases, and the ratio of the volume of phosphorus source gas introduced, the volume of silicon source gas introduced, and the mass of porous carbon is satisfied to be 120-170 L:420-600 L:1 kg; the flow rate of phosphorus source gas is gradually reduced from 1-1.4 L / min to 0-0.1 L / min, and the flow rate of silicon source gas is 1.5-2 L / min; (S3) finally introducing hydrocarbon gas for carbon coating to prepare a phosphorus-silicon co-doped silicon-carbon composite negative electrode material; The phosphorus source gas is phosphorus hydride.

2. The preparation method according to claim 1, characterized in that In step (S1), the specific surface area of ​​the porous carbon is 1400-2200m 2 / g, pore volume of 0.7-1.2cm 3 / g, the micropore ratio is 70-98%, and the porous carbon particle size is 5-20μm; the inert gas is one of nitrogen, argon and helium.

3. The preparation method according to claim 1, characterized in that In step (S2), the silicon source gas is selected from at least one of monosilane, disilane, dimethylsilane, dichlorodihydrosilane, and trichlorosilane.

4. The preparation method according to claim 1, characterized in that In step (S3), the hydrocarbon gas is selected from at least one of methane, ethane, propane, ethylene, propylene, and acetylene.

5. The preparation method according to claim 1, characterized in that The amount of hydrocarbon gas introduced satisfies the thickness of the carbon coating layer of 2-20 nm, or the ratio of the amount of hydrocarbon gas introduced to the mass of the porous carbon is 150-200 L: 1 kg.

6. A phosphorus-silicon co-doped silicon-carbon composite negative electrode material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 5.

7. A lithium-ion battery, characterized in that: The negative electrode comprises a phosphorus-silicon co-doped silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 1 to 5.

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