TWI845941B - Method for making element-doped silicon carbon composite anode materia - Google Patents

Abstract

The invention relates to an element-doped silicon carbon composite anode material, which comprises a plurality of element-doped silicon carbon composite abode material particles, and each element-doped silicon carbon composite anode material particle comprises an element-doped silicon nanoparticle, a first carbon coating layer and a second carbon coating layer, the element-doped silicon nanoparticle is a core, and the first carbon coating layer is coated on the surface of the element-doped silicon nanoparticle, the second carbon coating layer covers the first carbon coating layer, and the doping element is at least one of a IIIA group element, a VA group element and a transition metal element. The present invention further provides a preparation method for preparing the element-doped silicon carbon composite anode material.

Description

Preparation method of element-doped silicon-carbon composite negative electrode material

The present invention relates to an element-doped silicon-carbon composite negative electrode material and a preparation method thereof.

In recent years, silicon has been considered as a new generation of negative electrode material that is expected to replace graphite due to its advantages such as low cost, environmental protection, high specific capacity (4200mAh·g ^-1 ), slightly higher voltage platform than graphite, and no lithium metal deposition on the surface during charging. However, the volume of silicon material will expand dramatically (~300%) when lithium is embedded, and shrink dramatically when lithium is removed. This repeated and dramatic volume change (called volume effect) will cause the silicon material to crack and pulverize, resulting in structural collapse, causing the active material to peel off from the current collector and lose electrical contact, reducing the cycle stability of the battery. In addition, due to this volume effect, it is difficult for silicon to form a stable solid electrolyte interface (SEI) in the electrolyte. As the structure is destroyed, new silicon is exposed on the surface and continuously forms a SEI film, which will intensify the corrosion of silicon and cause the battery capacity to decay.

In order to alleviate the above problems and improve the electrochemical performance of silicon materials, previous technologies usually oxidize silicon materials to form silicon oxide shells. However, the electrical conductivity of silicon is 10 ³ Ω. m, and the electrical conductivity of the oxidized material (SiO _x ) is even lower, which seriously affects the charge transfer. Furthermore, using SiO _x to suppress expansion will increase the consumption of lithium ions due to electrochemical side reactions, resulting in the long cycle effect being affected.

In view of this, it is indeed necessary to provide an element-doped silicon-carbon composite negative electrode material and its preparation method to solve the above technical problems.

An element-doped silicon-carbon composite negative electrode material includes a plurality of element-doped silicon-carbon composite negative electrode material particles, each element-doped silicon-carbon composite negative electrode material particle includes an element-doped silicon nanoparticle, a first carbon coating layer and a second carbon coating layer, the element-doped silicon nanoparticle is a core, the first carbon coating layer is coated on the surface of the element-doped silicon nanoparticle, the second carbon coating layer covers the first carbon coating layer, and the doping element is one or more of Group IIIA elements, Group VA elements or transition metal elements.

The element-doped silicon-carbon composite negative electrode material contains no silicon oxide at all or almost no silicon oxide.

The mass percentage of silicon oxide in the element-doped silicon-carbon composite negative electrode material is less than or equal to 0.1%.

The element-doped silicon-carbon composite negative electrode material contains no oxide at all or almost no oxide.

A method for preparing an element-doped silicon-carbon composite negative electrode material comprises the following steps: in a protective environment, nano-forming a silicon material to obtain nano-silicon, or the protective environment is obtained by introducing an inert atmosphere or adding a solvent; in the protective environment, adding an appropriate amount of a doping element raw material to the nano-silicon, then adding a high molecular polymer, and fully stirring and mixing the nano-silicon, the doping element raw material and the high molecular polymer to obtain The doped nano-silicon material; in the presence of a high molecular polymer, a first carbon source is added to self-assemble, and then a second carbon source is added to self-assemble to obtain layered nano-silicon; in the protective environment, the layered nano-silicon is granulated to obtain a spherical precursor; the precursor is sintered in a reducing atmosphere or a vacuum environment at a sintering temperature of 800°C to 1100°C to obtain the silicon-carbon composite negative electrode material.

In a certain embodiment, the first carbon source includes at least one of asphalt, graphite and graphene. The first carbon source forms a layered first carbon coating layer. The first carbon coating layer coats the element-doped silicon nanoparticles inside, which can inhibit volume expansion and reduce volume effect. The second carbon source includes at least one of carbon black, carbon nanotubes and carbon nanofibers. The second carbon source forms a layered second carbon coating layer, and the second carbon coating layer coats the first carbon coating layer. The second carbon source has a higher electrical conductivity than the first carbon source, and the second carbon coating layer can provide charge transfer to increase the capacity.

The inert atmosphere includes at least one of argon, nitrogen and helium. The inert atmosphere can provide an oxygen-free environment to prevent nano-silicon from being oxidized, so that the prepared element-doped silicon-carbon composite negative electrode material does not contain silicon oxide materials, which is beneficial to improving the electrochemical properties of the element-doped silicon-carbon composite negative electrode material and reducing the volume effect.

The element-doped silicon-carbon composite negative electrode material and the preparation method thereof provided by the present invention have the following advantages: First, element doping can reserve space in the silicon lattice, providing the buffer space required when the silicon material volume expands during the cycle process, thereby greatly improving the cycle performance of the element-doped silicon-carbon composite negative electrode material. Second, the element-doped silicon-carbon composite negative electrode material does not contain oxides, and during the charge and discharge cycle process, there are no irreversible oxides to increase the consumption of lithium ions, thereby improving efficiency. Third, the element-doped silicon-carbon composite negative electrode material includes a first carbon coating layer and a second carbon coating layer. The first carbon coating layer is a buffer layer that can inhibit expansion; the second carbon coating layer is a conductive layer that can provide charge transfer to increase the capacitance and improve the electrochemical properties of the silicon-carbon composite negative electrode material. The method for preparing the element-doped silicon-carbon composite negative electrode material provided in this application is carried out in an atmosphere of protective gas, which can avoid the generation of oxides. Moreover, the process is simple, easy to control the process, and suitable for industrial production.

10: Element-doped silicon-carbon composite negative electrode material particles

102: Element-doped silicon nanoparticles

104: First carbon coating layer

106: Second carbon coating layer

108: Mixed elements

Figure 1 is a schematic diagram of the structure of the element-doped silicon-carbon composite negative electrode material particles provided in an embodiment of the present invention.

Figure 2 is a schematic diagram of the process of preparing the element-doped silicon-carbon composite negative electrode material provided in an embodiment of the present invention.

Figure 3 is a scanning electron microscope photograph of the surface of the element-doped silicon-carbon composite negative electrode material particles provided in an embodiment of the present invention.

Figure 4 is a comparison diagram of the XRD (X-ray diffraction) of the element-doped silicon-carbon composite negative electrode material provided in the embodiment of the present invention and the negative electrode material provided in the comparative example.

Figure 5 is a curve diagram of the lithium-stripping capacity, lithium-embedded capacity and efficiency obtained by the element-doped silicon-carbon composite negative electrode material provided in the embodiment of the present invention after the battery is assembled.

The following will further describe the element-doped silicon-carbon composite negative electrode material and its preparation method provided by the present invention in combination with the attached figures and specific embodiments. The following embodiments and features in the embodiments can be combined with each other without conflict.

The present invention provides an element-doped silicon-carbon composite negative electrode material, which includes a plurality of element-doped silicon-carbon composite negative electrode material particles. 1, the element-doped silicon-carbon composite negative electrode material particle 10 includes an element-doped silicon nanoparticle 102, a first carbon coating layer 104, and a second carbon coating layer 106. The element-doped silicon nanoparticle 102 is a core, the first carbon coating layer 104 is coated on the surface of the element-doped silicon nanoparticle 102, and the second carbon coating layer 106 covers the first carbon coating layer 104. The element-doped silicon nanoparticle 102 includes a silicon matrix (not shown) and a doping element 108 located in the silicon matrix. The doping element is one or more of Group IIIA elements, Group VA elements or transition metal elements.

The particle size of the element-doped silicon-carbon composite negative electrode material particles 10 is 10 microns to 20 microns. The shape of the element-doped silicon-carbon composite negative electrode material particles 10 can be spherical or quasi-spherical. The quasi-spherical shape means that its shape is close to a sphere, but not a strict sphere, and is an irregular shape. The particle size of the silicon nanoparticles 102 is 10 nanometers to 100 nanometers.

The doping element 108 may be a IIIA group element, such as boron (B), aluminum (Al), gallium (Ga), indium (In), tantalum (Tl), germanium (Ge), tin (Sn) or lead (Pb); it may also be a VA group element, such as nitrogen (N), phosphorus (P), arsenic (As), tellurium (Sb) or bismuth (Bi); it may also be a transition metal element, such as sc, titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), tantalum (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag) or cadmium (Cd), etc. The element doping can reserve space in the silicon lattice. When the element doped silicon-carbon composite negative electrode material is used as a negative electrode, during the cycle, the doping element 108 can provide the buffer space required when the silicon material volume expands, thereby greatly improving the cycle performance of the element doped silicon-carbon composite negative electrode material. Each element doped silicon-carbon composite negative electrode material particle 10 can include only one doping element 108, or two or more doping elements 108.

The element-doped silicon-carbon composite negative electrode material contains no silicon oxide at all or almost no silicon oxide.

The mass percentage of silicon oxide in the element-doped silicon-carbon composite negative electrode material is less than or equal to 0.1%.

The element-doped silicon-carbon composite negative electrode material contains no oxide at all or almost no oxide.

In one embodiment, the element-doped silicon-carbon composite negative electrode material particles 10 are composed of element-doped silicon nanoparticles 102, a first carbon coating layer 104 and a second carbon coating layer 106.

Since the element-doped silicon-carbon composite negative electrode material does not contain oxides, when the element-doped silicon-carbon composite negative electrode material is used as a negative electrode, there are no irreversible oxides to increase the consumption of lithium ions during the charge and discharge cycle, thereby improving the efficiency of the battery.

The material of the first carbon coating layer 104 includes at least one of asphalt, graphite and graphene. The first carbon coating layer 104 encapsulates element-doped silicon nanoparticles inside, which can inhibit volume expansion and reduce volume effect. The material of the second carbon coating layer 106 includes at least one of carbon black, carbon nanotubes and carbon nanofibers. The second carbon coating layer 106 encapsulates the first carbon coating layer 104. The second carbon coating layer 106 has a higher electrical conductivity than the first carbon coating layer 104, and the second carbon coating layer 106 can provide charge transfer to increase the capacity of the battery.

Please refer to FIG. 2. The present invention further provides a method for preparing an element-doped silicon-carbon composite negative electrode material, which comprises the following steps: S1: in a protective environment, nano-forming a silicon material to obtain nano-silicon, or the protective environment is obtained by introducing an inert gas or adding a solvent; S2: in the protective environment, adding an appropriate amount of a doping element raw material to the nano-silicon, and then adding a high molecular polymer to mix the nano-silicon, the doping element raw material and the high molecular polymer. The sub-polymer is stirred and mixed thoroughly; S3: In the presence of a high molecular polymer, a first carbon source is added to self-assemble, and then a second carbon source is added to self-assemble to obtain layered nanosilicon; S4: In the protective environment, the layered nanosilicon is granulated to obtain a spherical precursor; S5: The precursor is sintered in a reducing atmosphere or a vacuum environment at a sintering temperature of 800°C to 1100°C to obtain the silicon-carbon composite negative electrode material.

Below, each step of the preparation method of the element-doped silicon-carbon composite negative electrode material provided in the embodiment of the present invention will be introduced in detail.

S1: In a protective environment, the silicon material is nano-sized to obtain nano-silicon, or the protective environment is obtained by introducing an inert gas or adding a solvent.

In some embodiments, the silicon material may be semiconductor grade silicon material, and the particle size of the silicon material is greater than or equal to 10 microns. The implementation methods of nano-processing include but are not limited to mechanical processing, mechanical ball milling, etc., and the mechanical ball milling can be dry milling or wet milling. Nano-silicon can also be prepared by chemical method or physical vapor deposition method.

In some embodiments, the inert gas includes at least one of argon (Ar), nitrogen (N ₂ ) and helium (He). The inert gas can provide an oxygen-free environment to prevent the oxidation of nano-silicon, so that the prepared element-doped silicon-carbon composite negative electrode material does not contain silicon oxides, which is beneficial to improving the electrochemical properties of the element-doped silicon-carbon composite negative electrode material and reducing the volume effect.

In some embodiments, the solvent may be diethylene glycol (DEG), polyethylene glycol (PEG), propylene glycol (PG), dimethyl sulfoxide (DMSO) or a combination thereof. The solvent can prevent nanosilicon from being oxidized, so that the prepared element-doped silicon-carbon composite negative electrode material does not contain silicon oxide, which is beneficial to improving the electrochemical properties of the element-doped silicon-carbon composite negative electrode material and reducing the volume effect.

In some embodiments, the particle size of nanosilicon is 10nm~50nm. Nanosilicon is conducive to subsequent self-assembly and coating, and the preparation of silicon-carbon composite negative electrode materials with suitable particle sizes is suitable for the current secondary battery slurry process.

S2: In the protective environment, add an appropriate amount of raw materials of doping elements into nanosilicon, then add a polymer, and fully stir and mix the nanosilicon, raw materials of doping elements and polymer.

The raw material of the doping element can be solid, liquid or gaseous, which will be determined by the doping element. If the doping element is present, it can be in the form of a single substance or a compound. The doping element may be a IIIA group element, such as boron (B), aluminum (Al), gallium (Ga), indium (In), titania (Tl), germanium (Ge), tin (Sn) or lead (Pb); or a VA group element, such as nitrogen (N), phosphorus (P), arsenic (As), tellurium (Sb) or bismuth (Bi); or a transition metal element, such as stygium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), tantalum (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag) or cadmium (Cd). For example, when the doping element is a metal, it can be in a solid elemental form, and the raw material of the doping element can be metal particles.

In step S2, the method of fully stirring and mixing the nanosilicon, the doping element raw material and the high molecular polymer can be mechanical grinding or mechanical ball milling. During the stirring and mixing process, since the Mohs hardness of the doping material is lower than that of the silicon material, the particle refinement speed during the processing and grinding process will be faster than that of the silicon material.

In some embodiments, the polymer is an amphoteric polymer having both a hydrophobic group and a hydrophilic group. Furthermore, the polymer can be N-allyl-(2-ethylxanthate) propionamide (NAPA), dimethylformamide (DMF) or a combination thereof. In some embodiments, the polymer is a medium containing, for example, amino groups and hydroxyl groups.

S3: In the presence of a high molecular weight polymer, add the first carbon source to self-assemble, and then add the second carbon source to self-assemble to obtain layered nano-doped silicon.

In some embodiments, the first carbon source includes at least one of asphalt, graphite and graphene. The first carbon source is layered, and the carbon buffer layer formed by the first carbon source wraps the nanosilicon inside, which can inhibit volume expansion and reduce volume effect. In addition, during the self-assembly process, the particle escape phenomenon will trigger an exothermic reaction, and the first carbon source can perform thermal diffusion to avoid agglomeration and prevent the nanosilicon from being oxidized due to the exothermic phenomenon.

In some embodiments, the second carbon source includes at least one of carbon black, carbon nanotubes, and carbon nanofibers. The carbon conductive layer formed by the second carbon source can cover the carbon buffer layer. The second carbon source has a higher conductivity than the first carbon source. The carbon conductive layer can provide charge transfer to increase the capacity. In addition, during the self-assembly process, the particle escape phenomenon will trigger an exothermic reaction. The second carbon source can perform thermal diffusion to avoid agglomeration and prevent nanosilicon from being oxidized due to the exothermic phenomenon.

Steps S2 and S3 are both carried out in the presence of a polymer. Using a polymer, the doped element particles can be coated on the silicon surface first, and then the hydrophilic and hydrophobic properties of the two ends of the polymer can be used. The polymer chain at the hydrophobic end can be combined with the carbon substrate added later, so that the material undergoes silicon/doping, polymer, and carbon at the same time during the nano-process, completing orderly stacking self-assembly. The exothermic reaction caused by the escape of particles during the grinding process can also be thermally diffused through the carbon substrate in the solvent to avoid particle agglomeration and oxidation caused by thermal polymerization.

Furthermore, the homogenization self-assembly process may be, but is not limited to, mechanical processing, discharge processing or mechanical ball milling. Among them, mechanical ball milling can be dry milling or wet milling.

S4: In a protective environment, the layered doped nanosilicon is granulated to obtain a spherical precursor.

The specific process of granulation is a commonly used granulation method in this field, and this application does not limit it. Furthermore, the particle size of the spherical precursor obtained after granulation is 5μm~10μm, which is suitable for the current secondary battery pulping process and can also avoid agglomeration during the sintering process.

S5: Sinter the spherical precursor in a reducing atmosphere or vacuum environment at a sintering temperature of 800℃~1100℃ to obtain an element-doped silicon-carbon composite negative electrode material.

In some embodiments, the reducing atmosphere includes a nitrogen-hydrogen mixture. Sintering in a reducing atmosphere can remove excess functional groups on the surface, increase the density and integrity of the carbon substrate coating, and the reducing atmosphere can also prevent silicon from being oxidized (no oxide).

It is understandable that the purpose of numbering the steps is to clearly describe the specific preparation method, and it is not to limit the order of the steps.

In the preparation method of the element-doped silicon-carbon composite negative electrode material provided by the present invention, after completing the self-assembly multi-layering, the material can be made compact by granulation technology, reducing the dead lithium phenomenon caused by too many holes during the lithium ion activation process, and avoiding heat accumulation due to increased impedance during the charging process, thereby causing thermal runaway. The two-stage sintering process completes granulation at the same time, and the obtained material particles are solid spheres rather than hollow spheres, avoiding affecting the slurrying of the battery electrode. In a protective atmosphere environment, the generation of oxides in the element-doped silicon-carbon composite negative electrode material can be avoided, thereby increasing the compactness.

The advantages of the element-doped silicon-carbon composite negative electrode material and its preparation method provided by the present invention will be explained below through specific facts and test results.

Implementation Example 1

Select semiconductor grade silicon material (>10um) and put it into a grinder with a rotation speed of 2400~3000rpm for mechanical processing. At the same time, add diethylene glycol and 5wt% N-allyl-(2-ethylxanthate) propionamide (NAPA) polymerized polymer to grind the silicon material to 50~100nm. After the silicon material is ground to nanometer size, add doping element source material for doping. In this embodiment, the doping element is boron.

Add 10wt% flake natural graphite and then carbon black, and through the self-assembly process, nanosilicon can be compounded on the surface of the carbon substrate to obtain the precursor of the composite.

The precursor is placed in a sintering furnace containing nitrogen-hydrogen (or argon-hydrogen) mixed gas, with a gas flow rate of 2L/min, and heat treated at 950℃ for 8h. After heat treatment, a boron-doped silicon-carbon composite negative electrode material is obtained.

Please refer to Figure 3. XRD evidence shows that compared with the silicon-carbon composite material before doping, the peak position of the material after doping shifts to a lower angle of about 0.1°, indicating that the element doping affects the lattice constant, proving that the boron element is successfully doped into the silicon-carbon composite material, and a boron-doped silicon-carbon composite electrode material is obtained.

Please refer to Figure 4. The particle surface of the element-doped silicon-carbon composite negative electrode material obtained after sintering is smooth, showing a dense coating, and the specific surface area can be effectively controlled.

Further, according to the method provided in Example 1, phosphorus-doped silicon-carbon composite negative electrode materials and copper-doped silicon-carbon composite negative electrode materials were obtained respectively. The boron-doped silicon-carbon composite negative electrode material was recorded as sample 1, the phosphorus-doped silicon-carbon composite negative electrode material was recorded as sample 2, and the copper-doped silicon-carbon composite negative electrode material was recorded as sample 3. The three samples were dissolved in water with a conductive agent (conductive carbon black Super P) and a binder (styrene-butadiene rubber SBR) at a mass ratio of 88:1:11 to obtain a mixture, which was prepared into a slurry with a solid content of 50%. The slurry is coated on a copper foil current collector and vacuum dried to obtain a negative electrode. Then the conventional production process is used to assemble the ternary positive electrode, the electrolyte with a lithium salt concentration of 1 mol/L (composed of LiPF ₆ /EC+DMC+EMC), and the Celgard2400 diaphragm for soft pack battery stacking and 5Ah assembly. The battery assembled from sample 1 is recorded as battery 1, the battery assembled from sample 2 is recorded as battery 2, and the battery assembled from sample 3 is recorded as battery 3. In addition, a comparative battery 4 is added, and the negative electrode material used in the comparative battery 4 is an undoped silicon-carbon composite material. Battery 1, battery 2, battery 3 and battery 4 are respectively subjected to the following performance tests.

The above battery was subjected to negative electrode lithium ion de-lithiation capacity test (De-Lithiation): current density 0.1C, voltage dropped to 2.0V, and then the negative electrode gram capacitance was converted according to the following formula to obtain the de-lithiation capacity.

Please refer to Table 1 for performance test results.

As shown in Table 1, the element-doped silicon-carbon composite negative electrode material provided in the embodiment of the present invention can improve the cycle performance of the battery, and the capacity retention rate after 100 cycles is more than 90%. This shows that the element-doped silicon-carbon composite negative electrode material prepared in this application can inhibit volume expansion and improve conductivity and capacity.

Furthermore, the lithium stripping capacity and lithium embedding capacity of the battery 1 prepared by the boron-doped silicon-carbon composite negative electrode material provided in the embodiment of the present invention were tested simultaneously, and the results shown in Figure 5 were obtained. Among them, efficiency = lithium stripping capacity/lithium embedding capacity × 100%. It can be seen from Figure 5 that the lithium stripping capacity and lithium embedding capacity of the battery 1 prepared by the boron-doped silicon-carbon composite negative electrode material provided in the embodiment of the present invention are almost the same, so the battery has a high efficiency, almost reaching 100%.

The element-doped silicon-carbon composite negative electrode material and the preparation method thereof provided by the present invention have the following advantages: First, element doping can reserve space in the silicon lattice, providing the buffer space required when the silicon material volume expands during the cycle process, thereby greatly improving the cycle performance of the element-doped silicon-carbon composite negative electrode material. Second, the element-doped silicon-carbon composite negative electrode material does not contain oxides, and during the charge and discharge cycle process, there are no irreversible oxides to increase the consumption of lithium ions, thereby improving efficiency. Third, the element-doped silicon-carbon composite negative electrode material includes a first carbon coating layer and a second carbon coating layer. The first carbon coating layer is a buffer layer that can inhibit expansion; the second carbon coating layer is a conductive layer that can provide charge transfer to increase the capacitance and improve the electrochemical properties of the silicon-carbon composite negative electrode material. The method for preparing the silicon-carbon composite negative electrode material in this application is carried out in an atmosphere of protective gas, which can avoid the generation of oxides. Moreover, the process is simple, easy to control the process, and suitable for industrial production.

In summary, this invention has indeed met the requirements for invention patents, so a patent application has been filed in accordance with the law. However, the above is only a preferred embodiment of this invention, and it cannot be used to limit the scope of the patent application of this case. Any equivalent modifications or changes made by people familiar with the art of this case based on the spirit of this invention should be included in the scope of the following patent application.

10: Element-doped silicon-carbon composite negative electrode material particles

102: Element-doped silicon nanoparticles

104: First carbon coating layer

106: Second carbon coating layer

108: Mixed elements

Claims (10)

A method for preparing an element-doped silicon-carbon composite negative electrode material comprises the following steps: S1: in a protective environment, nano-forming a silicon material to obtain nano-silicon, wherein the protective environment is obtained by introducing an inert gas or adding a solvent; S2: in the protective environment, adding an appropriate amount of a doping element raw material to the nano-silicon, and then adding a high molecular polymer, and fully stirring and mixing the nano-silicon, the doping element raw material and the high molecular polymer. ; S3: adding a first carbon source to the polymer for self-assembly, and then adding a second carbon source for self-assembly to obtain layered nanosilicon; S4: granulating the layered nanosilicon in the protective environment to obtain a spherical precursor; and S5: sintering the precursor in a reducing atmosphere or a vacuum environment at a sintering temperature of 800°C to 1100°C to obtain the silicon-carbon composite negative electrode material. A method for preparing an element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein the silicon material may be semiconductor-grade silicon material, and the particle size of the silicon material is greater than or equal to 10 microns. A method for preparing an element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein the solvent is one or more of diethylene glycol (DEG), polyethylene glycol (PEG), propylene glycol (PG), and dimethyl sulfoxide (DMSO). A method for preparing an element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein the polymer is an amphoteric polymer having both a hydrophobic group and a hydrophilic group. A method for preparing an element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein the doping element is boron (B), aluminum (Al), gallium (Ga), indium (In), tantalum (Tl), germanium (Ge), tin (Sn), lead (Pb), nitrogen (N), phosphorus (P), arsenic (As), tellurium (Sb), bismuth (Bi), styrene (Sc), titanium One or more of titanium, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), terbium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag) or cadmium (Cd). The method for preparing the element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein steps S2 and S3 are both performed in the presence of a high molecular polymer. The method for preparing the element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein in step S4, the particle size of the spherical precursor obtained after granulation is 5μm~10μm. A method for preparing an element-doped silicon-carbon composite negative electrode material as described in claim 1, wherein the first carbon source includes at least one of asphalt, graphite and graphene; and the second carbon source includes at least one of carbon black, carbon nanotubes and carbon nanofibers. An element-doped silicon-carbon composite negative electrode material obtained by the preparation method described in any one of claims 1 to 8, wherein the mass percentage of silicon oxide in the element-doped silicon-carbon composite negative electrode material is less than or equal to 0.1%. The element-doped silicon-carbon composite negative electrode material as described in claim 9, wherein the particle size of the element-doped silicon-carbon composite negative electrode material particles is 10 microns to 20 microns.