Silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of electrode materials, in particular to a silicon-carbon negative electrode material and a preparation method and application thereof. The silicon-carbon negative electrode material comprises a plurality of silicon-carbon composite particles, each silicon-carbon composite particle comprises porous carbon, nano silicon particles and phosphorus element which are attached in pores of the porous carbon, and coating carbon for coating the porous carbon, and n-type doping of the phosphorus element is formed at the joint of the nano silicon particles and the porous carbon. The preparation method comprises the following steps: (1) adsorbing phosphoric acid in porous carbon, and carrying out a heating reaction in a protective gas atmosphere to generate phosphorus-infiltrated porous carbon; (2) introducing a gaseous silicon source in a protective gas atmosphere, and carrying out silicon deposition on the phosphorus-infiltrated porous carbon by adopting a chemical vapor deposition method to obtain a phosphorus-doped silicon carbon material; and (3) carrying out carbon coating on the phosphorus-doped silicon carbon material to obtain the phosphorus-doped silicon carbon material. According to the method, the rate capability of the silicon-carbon negative electrode material can be remarkably improved while high first efficiency and high gram capacity are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and more particularly, to a silicon-carbon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, graphite is commonly used as the anode material for lithium-ion batteries. However, the low lithium storage capacity of graphite itself has been difficult to meet the requirements of high-capacity density and high power. Silicon, with its high lithium storage capacity (3580 mAh / g), low lithium intercalation potential, and abundant reserves, has become an ideal anode material for the new generation of lithium-ion batteries.

[0003] However, pure silicon undergoes excessive volume expansion during the lithium ion insertion / extraction process, which limits the application of silicon anodes. The silicon-carbon composite anode material prepared by infiltrating silicon into porous carbon, as a new type of silicon-containing anode, has a smaller volume effect and better cycling performance than pure silicon. One of the main problems of the currently prepared silicon-carbon composite anode material by infiltrating silicon into porous carbon is its poor rate performance.

[0004] Existing technical literature:

[0005] Patent Document 1: Chinese Patent with Publication No. CN115668545A discloses a process for infiltrating silicon into porous carbon;

[0006] Patent Document 2: Chinese Patent with Publication No. CN116259726A discloses the doping of silicon with phosphine and phosphorus oxychloride;

[0007] Patent Document 3: Chinese Patent with Publication No. CN116344807A discloses the doping of silicon with phosphine and phosphorus oxychloride. Summary of the Invention

[0008] The inventors of the present invention have found through in-depth research that:

[0009] The process of Patent Document 1 only uses acetylene cracking coating on the surface of porous carbon after the infiltration of silicon into porous carbon, which only improves the electronic conductivity on the surface of the silicon-carbon anode material particles and cannot effectively improve the rate performance of such silicon-carbon anode materials. Although Patent Documents 2 and 3 improve the overall electronic conductivity of the material, the phosphine they selected is too toxic and easily reacts with equipment to form phosphides under hot conditions. Phosphorus oxychloride also has medium toxicity, and the phosphorus pentoxide generated by its decomposition under high-temperature conditions can react with silicon to form silicon dioxide, thereby reducing the initial efficiency and specific capacity of the overall material.

[0010] In view of this, the present invention is specifically proposed.

[0011] The first object of the present invention is to provide a silicon-carbon anode material, which has good rate performance, high capacity, and high initial efficiency.

[0012] The second object of the present invention is to provide a preparation method of the silicon-carbon negative electrode material as described above. In this method, porous carbon adsorbs phosphoric acid and reacts at high temperature to generate elemental phosphorus, which adheres to the inner surface of the porous carbon. During the process of chemical vapor deposition of silicon, elemental phosphorus diffuses into the silicon for doping, improving the electronic conductivity of silicon. Moreover, oxygen is not introduced during the silicon infiltration process, ensuring high initial efficiency and high specific capacity while improving the rate performance of the negative electrode material.

[0013] The third object of the present invention is to provide a negative electrode sheet, which includes the silicon-carbon negative electrode material as described above.

[0014] The fourth object of the present invention is to provide a lithium-ion battery, which includes the negative electrode sheet as described above.

[0015] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0016] A silicon-carbon negative electrode material includes a plurality of silicon-carbon composite particles. The silicon-carbon composite particles include porous carbon, nano-silicon particles and phosphorus element adhering to the pores of the porous carbon, and coating carbon covering the porous carbon. The nano-silicon particles form n-type doping of phosphorus element at the junction with the porous carbon.

[0017] Preferably, the content of the phosphorus element is 0.1 wt% - 0.3 wt%.

[0018] Preferably, the porous carbon includes micropores, and the microporosity of the porous carbon is 77% - 99%.

[0019] Preferably, the particle size of the nano-silicon particles is <0.1 μm; preferably, the particle size of at least part of the nano-silicon particles is <5 nm.

[0020] Preferably, the content of the nano-silicon particles is 40 wt% - 60 wt%.

[0021] A preparation method of the silicon-carbon negative electrode material as described above includes the following steps:

[0022] (1) Adsorb phosphoric acid in the porous carbon, and carry out a heating reaction under a protective gas atmosphere to generate phosphorus-infiltrated porous carbon;

[0023] (2) Under a protective gas atmosphere, introduce a gaseous silicon source, and carry out silicon deposition on the phosphorus-infiltrated porous carbon by chemical vapor deposition to obtain a phosphorus-doped silicon-carbon material;

[0024] (3) Carry out carbon coating on the phosphorus-doped silicon-carbon material to obtain the silicon-carbon negative electrode material.

[0025] Preferably, in step (1), the temperature of the heating reaction is 800 - 1000 °C, and the time of the heating reaction is 2 - 4 h.

[0026] Preferably, the method for adsorbing the phosphoric acid into the porous carbon includes the following steps:

[0027] The porous carbon is soaked in a phosphoric acid solution and then subjected to solid-liquid separation to obtain the porous carbon adsorbed with the phosphoric acid.

[0028] Preferably, the mass concentration of the phosphoric acid solution is 40 wt% - 85 wt%.

[0029] Preferably, the soaking time of the porous carbon in the phosphoric acid solution is 0.5 - 2 h.

[0030] Preferably, the solid-liquid separation method is centrifugal separation.

[0031] Preferably, in step (2), the gaseous silicon source includes at least one of silane, disilane, trichlorosilane, dichlorosilane, propylsilane, trichlorosilane, and silicon chloride.

[0032] Preferably, in step (2), the temperature of silicon deposition is 400 - 500 °C, and the time of silicon deposition is 6 - 10 h.

[0033] Preferably, the flow rate ratio of the gaseous silicon source to the protective gas is 2 - 4:1.

[0034] Preferably, the carbon coating is carried out by chemical vapor deposition. Under the atmosphere of the protective gas, a gaseous carbon source is introduced to carry out carbon coating on the phosphorus-doped silicon-carbon material.

[0035] Preferably, the gaseous carbon source includes at least one of acetylene, methane, ethane, and ethylene.

[0036] Preferably, the temperature of the carbon coating is 500 - 600 °C, and the time of the carbon coating is 1 - 3 h.

[0037] A negative electrode sheet, which includes the silicon-carbon negative electrode material as described above.

[0038] A lithium-ion battery, which includes the negative electrode sheet as described above.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] (1) In the method of the present invention, phosphoric acid is adsorbed inside the porous carbon. At high temperature, phosphorus pentoxide decomposed from phosphoric acid reacts with carbon to generate elemental phosphorus, which adheres to the inner surface of the porous carbon. During the process of gas-phase silicon deposition, the elemental phosphorus adhering to the inner surface of the porous carbon diffuses into the silicon, and phosphorus doping is formed at the junction of silicon and porous carbon, improving the electronic conductivity of silicon, and further improving the overall electronic conductivity of the material, thereby improving the rate performance of the silicon-carbon anode material.

[0041] (2) The method of the present invention utilizes the adsorption performance of porous carbon to improve the uniformity of phosphorus distribution. At high temperature, phosphorus pentoxide and the generated elemental phosphorus may volatilize. Since there are unbalanced and unsaturated molecular attractions on the solid surface in the porous carbon, which can adsorb gases, the volatilized phosphorus pentoxide and phosphorus can be adsorbed by the porous carbon again, making the phosphorus distribution more uniform.

[0042] (3) The method of the present invention does not introduce oxygen during the silicon deposition process (the decomposition product of phosphoric acid at high temperature will react with carbon to generate elemental phosphorus and carbon dioxide, and the gas carbon dioxide molecules will be carried away by the protective gas), thereby ensuring high initial efficiency and high specific capacity while improving the rate performance.

[0043] (4) The raw materials used in the method of the present invention have low toxicity, high safety, and low corrosiveness to equipment.

[0044] (5) The silicon-carbon anode material provided by the present invention has good rate performance, high capacity, and high initial efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 It is the X-ray diffraction (XRD) pattern of the anode material prepared in Example 3 of the present invention;

[0047] Figure 2 It is the scanning electron microscope image of the anode material prepared in Example 3 of the present invention;

[0048] Figure 3 It is the scanning electron microscope image of the section of the anode material prepared in Example 3 of the present invention;

[0049] Figure 4 It is the charge-discharge curves at different rates of Examples 1-3 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they shall be carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0051] The first aspect of the present invention provides a silicon-carbon negative electrode material, which includes a plurality of silicon-carbon composite particles. The silicon-carbon composite particles include porous carbon, nano-silicon particles and phosphorus elements attached to the pores of the porous carbon, and coating carbon coating the porous carbon. The nano-silicon particles form an n-type doping of phosphorus elements at the junction thereof with the porous carbon.

[0052] The silicon-carbon negative electrode material provided by the present invention can improve the rate performance, capacity and initial efficiency of lithium-ion batteries. The nano-silicon particles are attached to the pores of the porous carbon, which can effectively alleviate the volume expansion of the silicon-carbon negative electrode material during the lithium-ion insertion / extraction process. Since silicon is a semiconductor material, with a small amount of doping of silicon, its conductivity can increase by several orders of magnitude. By forming an n-type doping of phosphorus elements at the junction of the nano-silicon particles and the porous carbon, the rate performance of the silicon-carbon negative electrode material can be significantly improved. Moreover, the solubility of phosphorus in silicon is very low, and doping a small amount of phosphorus elements can slightly damage the structure of the porous carbon and can also better control the cost.

[0053] In some specific embodiments of the present invention, the content of the phosphorus element is 0.1 wt% to 0.3 wt%, such as any value among 0.1 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.18 wt%, 0.21 wt%, 0.25 wt%, 0.3 wt% or a range value composed of any two of these values. If the content of the phosphorus element is too small, the impact on the capacity, initial efficiency and cycle performance is small, and the improvement effect is not obvious. If the content of the phosphorus element is too large, it is easy to cause a sharp drop in the microporosity, resulting in a significant reduction in the silicon infiltration amount, and thus a reduction in the capacity and initial efficiency.

[0054] In some specific embodiments of the present invention, the porous carbon includes micropores, and the microporosity of the porous carbon is 77% - 99%, such as any value among 77%, 80%, 85%, 90%, 95%, 99% or the range value composed of any two of these values. Using the porous carbon with high microporosity as the carrier greatly improves the adsorption capacity for phosphorus, effectively increases the doping space of silicon nanoparticles by elemental phosphorus, and further improves the doping amount of elemental phosphorus. However, too high a value will lead to a relatively high silicon infiltration amount, resulting in a loss of the initial efficiency capacity; and too low a microporosity will lead to a significant reduction in the silicon infiltration content under the same conditions, causing capacity loss.

[0055] In some specific embodiments of the present invention, the particle size of the nano-silicon particles < 0.1 μm; preferably, the particle size of at least part of the nano-silicon particles < 5 nm.

[0056] In some specific embodiments of the present invention, the content of the nano-silicon particles is 40 wt% - 60 wt%, such as any value among 40 wt%, 42 wt%, 45 wt%, 46.69 wt%, 47.67 wt%, 48.71 wt%, 49.05 wt%, 51.26 wt%, 55 wt%, 60 wt% or the range value composed of any two of these values; too low a silicon content will lead to capacity loss, and too much silicon content is likely to accumulate on the surface of the porous carbon, forming a silicon shell, resulting in poor uniformity of silicon distribution, and is likely to generate silicon carbide during the carbon coating process, leading to a decline in the initial efficiency and rate performance. Therefore, it is necessary to reasonably control the content of the nano-silicon particles.

[0057] The second aspect of the present invention provides a preparation method of a silicon-carbon negative electrode material, comprising the following steps:

[0058] (1) Adsorb phosphoric acid inside the porous carbon, and carry out a heating reaction under a protective gas atmosphere to generate phosphorus-impregnated porous carbon;

[0059] (2) Under a protective gas atmosphere, introduce a gaseous silicon source, and carry out silicon deposition on the phosphorus-impregnated porous carbon by chemical vapor deposition to obtain a phosphorus-doped silicon-carbon material;

[0060] (3) Carry out carbon coating on the phosphorus-doped silicon-carbon material to obtain the silicon-carbon negative electrode material.

[0061] In the method of the present invention, phosphoric acid is adsorbed inside the porous carbon. Under high-temperature conditions, phosphorus pentoxide decomposed from phosphoric acid reacts with carbon to generate elemental phosphorus, which adheres to the inner surface of the porous carbon. During the gas-phase silicon deposition process, the elemental phosphorus adhering to the inner surface of the porous carbon diffuses into the silicon, and phosphorus doping (n-type doping) is formed at the junction of silicon and porous carbon, improving the electronic conductivity of silicon, thereby improving the rate performance of the silicon-carbon negative electrode material.

[0062] The porous carbon can perform secondary adsorption on volatile phosphorus pentoxide and elemental phosphorus, improve the uniformity of phosphorus distribution, avoid the formation of silicon dioxide, increase the content of elemental phosphorus, increase the doping amount of silicon, effectively improve the initial efficiency and rate performance, and has a high specific capacity.

[0063] The method of the present invention uses phosphoric acid as the phosphorus source, which has low toxicity, high safety, and low corrosion to equipment.

[0064] In some specific embodiments of the present invention, in step (1), the temperature of the heating reaction is 800 - 1000 °C, such as any one value or the range value composed of any two values among 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C; the time of the heating reaction is 2 - 4 h, such as any one value or the range value composed of any two values among 2 h, 2.5 h, 3 h, 3.5 h, 4 h.

[0065] The present invention controls the temperature of the heating reaction at 800 - 1000 °C, effectively ensuring the full reduction reaction of by - product phosphorus pentoxide and carbon, and at the same time ensuring that the microporous structure of the porous carbon does not change significantly, and the microporosity decreases by less than 3%, effectively ensuring the subsequent silicon infiltration amount.

[0066] In some specific embodiments of the present invention, in step (1), the heating reaction is carried out in a rotary kiln. The steps are as follows: Put the porous carbon adsorbed with phosphoric acid into the rotary kiln, evacuate with a protective gas before heating. The protective gas is an inert gas. As an example, the protective gas can be nitrogen, and the nitrogen flow rate is 4 - 6 L / min for evacuation for 1 - 3 h, then reduce the nitrogen flow rate to 0.5 - 1.5 L / min, and heat to the target temperature at a heating rate of 3 - 8 °C / min for the heating reaction.

[0067] In some specific embodiments of the present invention, the method of adsorbing the phosphoric acid in the porous carbon includes the following steps:

[0068] Soak the porous carbon in a phosphoric acid solution and then separate the solid and liquid to obtain the porous carbon adsorbed with the phosphoric acid.

[0069] In some specific embodiments of the present invention, the mass concentration of the phosphoric acid solution is 40wt% - 85wt%, such as any one value or the range value composed of any two values among 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, 85wt%. The mass concentration of the phosphoric acid solution affects the adsorption amount of P in the porous carbon and needs to be controlled within a suitable range.

[0070] In some specific embodiments of the present invention, the soaking time of the porous carbon in the phosphoric acid solution is 0.5 - 2 h, such as any one value or the range value composed of any two values among 0.5 h, 1 h, 1.5 h, 2 h.

[0071] In some specific embodiments of the present invention, the solid-liquid separation method is centrifugal separation, and this process step can reduce the solid-liquid separation time and shorten the production cycle.

[0072] In some specific embodiments of the present invention, in step (2), the gaseous silicon source includes at least one of silane, disilane, trichlorosilane, dichlorosilane, propylsilane, trichlorosilane, and silicon chloride; in some embodiment modes, the silicon source that is liquid at room temperature can participate in the reaction in the form of steam.

[0073] In some specific embodiments of the present invention, in step (2), the temperature of silicon deposition is 400 - 500 °C, such as any value among 400 °C, 420 °C, 440 °C, 450 °C, 460 °C, 480 °C, 500 °C or the range value composed of any two of these values; the time of silicon deposition is 6 - 10 h, such as any value among 6 h, 7 h, 8 h, 9 h, 10 h or the range value composed of any two of these values.

[0074] In some specific embodiments of the present invention, the silicon deposition is carried out in a rotary furnace. After the heating reaction in step (1) is completed, it is naturally cooled to the target temperature, and a gaseous silicon source is introduced into the rotary furnace for chemical vapor deposition. A protective gas is continuously introduced during the silicon deposition process. As an example, the protective gas used is nitrogen.

[0075] In some specific embodiments of the present invention, the flow rate ratio of the gaseous silicon source to the protective gas is 2 - 4:1, such as any value among 2:1, 3:1, 4:1 or the range value composed of any two of these values.

[0076] In some specific embodiments of the present invention, the carbon coating is carried out by chemical vapor deposition method. Under the atmosphere of a protective gas, a gaseous carbon source is introduced to carry out carbon coating on the phosphorus-doped silicon-carbon material.

[0077] In some specific embodiments of the present invention, the carbon coating is carried out in a rotary furnace. After the silicon deposition in step (2) is completed, the introduction of the gaseous silicon source is stopped, the flow rate of the protective gas remains unchanged, it is adjusted to the target temperature, and a gaseous carbon source is introduced for vapor deposition. The flow rate of the gaseous carbon source is 0.5 L / min - 1.5 L / min.

[0078] In some specific embodiments of the present invention, the gaseous carbon source includes at least one of acetylene, methane, ethane, and ethylene.

[0079] In some specific embodiments of the present invention, the temperature of carbon coating is 500 - 600 °C, such as any one value among 500 °C, 540 °C, 550 °C, 560 °C, 580 °C, 600 °C or a range value composed of any two of these values; the time of carbon coating is 1 - 3 h, such as any one value among 1 h, 1.5 h, 2 h, 2.5 h, 3 h or a range value composed of any two of these values.

[0080] The third aspect of the present invention provides a negative electrode sheet, which comprises the silicon-carbon negative electrode material described in any one of the foregoing embodiments or the silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material described in any one of the foregoing embodiments.

[0081] The fourth aspect of the present invention provides a lithium-ion battery, which comprises the negative electrode sheet as described above.

[0082] The lithium-ion battery provided by the present invention has the advantages of good rate performance, high capacity and high initial efficiency.

[0083] The following will describe in detail some embodiments of the present invention in conjunction with specific examples. The raw materials used in the examples can be obtained through commercial purchase without special instructions.

[0084] Example 1

[0085] (1) 2 kg of porous carbon with a porosity of 80% was put into a phosphoric acid solution with a concentration of 40 wt% and soaked for 1 h. After centrifugal separation, the obtained solid material was put into a rotary furnace. The nitrogen flow rate was 5 L / min to evacuate for 2 h, then the nitrogen flow rate was reduced to 1 L / min, and the temperature was raised to 1000 °C at a heating rate of 5 °C / min and kept for 2 h for heating reaction to obtain phosphorus-impregnated porous carbon;

[0086] (2) After the heating reaction was completed, the temperature was naturally reduced to 450 °C, and silane (SiH4) was introduced into the cavity of step (1), and silicon deposition was carried out by chemical vapor deposition method. Among them, the flow rate ratio of silane to nitrogen was 3:1, and the vapor deposition was carried out for 8 h;

[0087] (3) After the silicon deposition was completed, the valve of silane was closed, the nitrogen flow rate remained unchanged, the temperature was raised to 550 °C at 5 °C / min, and acetylene was introduced with an acetylene flow rate of 1 L / min. The vapor deposition was carried out for 2 h, and then it was naturally cooled and discharged to obtain the silicon-carbon negative electrode material.

[0088] Example 2

[0089] Example 2 is similar to Example 1, the only difference being that: the mass concentration of the phosphoric acid solution used in Example 2 is 60 wt%, and the other conditions are the same as those in Example 1.

[0090] Example 3

[0091] Example 3 is similar to Example 1, except that: the mass concentration of the phosphoric acid solution used in Example 3 is 85 wt%, and the other conditions are the same as those in Example 1.

[0092] Example 4

[0093] Example 4 is similar to Example 1, except that: the microporosity of the porous carbon used in Example 4 is 99%, and the other conditions are the same as those in Example 1.

[0094] Example 5

[0095] Example 5 is similar to Example 1, except that: the microporosity of the porous carbon used in Example 5 is 77%, and the other conditions are the same as those in Example 1.

[0096] Comparative Example 1

[0097] (1) Put the porous carbon with a microporosity of 80% into the CVD gas deposition furnace, use a vacuum pump to evacuate to -0.1 MPa under negative pressure, empty with a nitrogen flow rate of 5 L / min for 1 h, heat up to 450 °C at a rate of 5 °C / min, reduce the nitrogen flow rate to 1 L / min, and introduce silane (SiH4) gas. Carry out silicon deposition by chemical vapor deposition method, where the flow rate ratio of silane to nitrogen is 3:1, and carry out gas deposition for 8 h;

[0098] (2) After the silicon deposition is completed, close the valve of silane, keep the nitrogen flow rate unchanged, heat up to 550 °C at a rate of 5 °C / min, introduce acetylene, and the acetylene flow rate is 1 L / min. Carry out gas deposition for 2 h, cool naturally, and cool and discharge to obtain the silicon-carbon negative electrode material.

[0099] Comparative Example 2

[0100] Comparative Example 2 is similar to Example 1, except that: the mass concentration of the phosphoric acid solution used in Comparative Example 2 is 95 wt%, and the other conditions are the same as those in Example 1.

[0101] Experimental Example

[0102] (1) Carry out XRD test on the negative electrode material prepared in Example 3, and carry out SEM test on the negative electrode material and the sliced samples in Example 3. The results are as Figure 1 、 Figure 2 and Figure 3 shown.

[0103] (2) Use a BET tester to test the BET and microporosity of the products at different stages in each example and each comparative example. The results are shown in Table 1.

[0104] Table 1

[0105]

[0106] (3) The phosphorus content of the products obtained in each example and each comparative example was tested using an ICP tester; the oxygen content of the products obtained in each example and each comparative example was tested using an oxygen content analyzer; the samples were calcined in air at 1000 °C for 1 h using a thermogravimetric analyzer to completely calcine the carbon and completely convert the silicon into silicon dioxide, and then the silicon content in the silicon-carbon material was calculated using the weight of the increased oxygen. The results are shown in Table 2.

[0107] Table 2

[0108] Number P content (wt%) Si content (wt%) O content (wt%) Example 1 0.12 49.05 0 Example 2 0.14 48.71 0 Example 3 0.21 47.67 0 Example 4 0.13 51.26 0 Example 5 0.10 46.69 0 Comparative Example 1 0 49.13 0 Comparative Example 2 0.31 45.22 0

[0109] (4) Battery assembly and electrochemical performance testing

[0110] Preparation of the battery:

[0111] The silicon-carbon anode materials prepared in each example and each comparative example were mixed according to the mass ratio of silicon-carbon anode material (anode active material): polyacrylic acid resin (PAA): single-walled carbon nanotube (CNT): conductive carbon black (SP) of 82:7:1:10, made into a slurry with deionized water, uniformly coated on a copper foil, and vacuum dried at 80 °C for 24 h to obtain the battery electrode sheets for the experiment. Then, a lithium sheet was used as the counter electrode, and an electrolyte of 1.1 mol / L LiPF6 with a solvent of a four-component mixed solvent, ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 1:1:1:1, and a polypropylene microporous membrane was used as the separator to assemble a CR2025-type coin-shaped half-cell in a vacuum glove box.

[0112] Constant current charge-discharge tests were carried out on a BlueTester, and the charge-discharge steps were: constant current discharge at 0.1C to 5 mV, then constant current discharge at 0.02C to 5 mV, and constant current charge at 0.1C to 2V.

[0113] The electrochemical performance results are shown in Table 3.

[0114] Table 3

[0115]

[0116] As can be seen from the data in Table 1, Table 2 and Table 3, for the porous carbon with a microporosity of 80.05%, as the phosphorus content increases (0.1 wt% - 0.3 wt%), both the BET and the microporosity of the phosphorus-impregnated porous carbon show a slight decrease. This is caused by the reaction between carbon and phosphorus pentoxide. Due to the decrease in microporosity, the amount of silicon impregnated under the same process conditions shows a slight decrease. This is because the decrease in microporosity causes a slight decrease in the adsorption capacity of the porous carbon. However, all the above changes are very slight. After phosphorus impregnation and then silicon impregnation to form phosphorus doping, the rate performance of the anode material is significantly improved, and the specific capacity, initial efficiency and stability are also improved.

[0117] However, if the phosphorus content exceeds 0.3 wt%, a large amount of phosphorus pentoxide generated will react with carbon, destroying the microporous structure, thus significantly reducing the microporosity, weakening the adsorption capacity for nano-silicon particles, and causing capacity loss. Therefore, when the P content exceeds 0.3 wt%, although the rate performance is improved, its specific capacity is significantly reduced, resulting in a decrease in the comprehensive performance of the battery.

[0118] In summary, compared with the silicon-carbon anode material prepared by the traditional method, the silicon-carbon anode material prepared by the method of the present invention significantly improves the rate performance of the silicon-carbon anode material while ensuring high initial efficiency and high specific capacity.

[0119] By analyzing the anode materials of all examples through XPS, in the high-resolution Si 2p spectrum, an n-type silicon characteristic peak at 100 eV can be found, indicating that there are phosphorus atoms in the silicon lattice, realizing phosphorus doping.

[0120] From Figure 1 it can be seen that silicon in the silicon-carbon anode material mainly exists in an amorphous form, proving that phosphorus doping does not affect the crystal growth of nano-silicon. From Figure 2 it can be seen that the surface of the particles is flat and smooth, and phosphorus doping does not affect the surface morphology of the material. From Figure 3 it can be seen that the phosphorus-doped nano-silicon is evenly distributed in the porous carbon.

[0121] From Figure 4 it can be seen that the rate performance of the examples is significantly better than that of the comparative examples, and the rate performance of the silicon-carbon anode material prepared by the method of the present invention has been significantly improved.

[0122] Although the present invention has been illustrated and described with reference to specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same; those of ordinary skill in the art should understand that without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A silicon-carbon anode material, characterized in that, It includes a plurality of silicon-carbon composite particles, and the silicon-carbon composite particles include porous carbon, nano-silicon particles and phosphorus elements attached to the pores of the porous carbon, and coated carbon coating the porous carbon, and the nano-silicon particles form n-type doping of phosphorus elements at the joint thereof with the porous carbon.

2. The silicon-carbon anode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (4): (1) The content of the phosphorus element is 0.1 wt% to 0.3 wt%; (2) The porous carbon includes micropores, and the microporosity of the porous carbon is 77% to 99%; (3) The particle size of the nano-silicon particles < 0.1 μm; preferably, the particle size of at least part of the nano-silicon particles < 5 nm; (4) The content of the nano-silicon particles is 40 wt% - 60 wt%.

3. A method for preparing the silicon-carbon anode material as described in claim 1 or 2, characterized in that, It includes the following steps: (1) Adsorb phosphoric acid in the porous carbon, and perform a heating reaction under a protective gas atmosphere to generate phosphorus-impregnated porous carbon; (2) Under a protective gas atmosphere, introduce a gaseous silicon source, and perform silicon deposition on the phosphorus-impregnated porous carbon by chemical vapor deposition to obtain a phosphorus-doped silicon-carbon material; (3) Perform carbon coating on the phosphorus-doped silicon-carbon material to obtain the silicon-carbon negative electrode material.

4. The preparation method of the silicon-carbon anode material according to claim 3, wherein In step (1), the temperature of the heating reaction is 800 - 1000 °C, and the time of the heating reaction is 2 - 4 h.

5. The preparation method of the silicon-carbon anode material according to claim 3, characterized in that, The method for adsorbing the phosphoric acid in the porous carbon includes the following steps: Soak the porous carbon in a phosphoric acid solution and then perform solid-liquid separation to obtain the porous carbon adsorbed with the phosphoric acid.

6. The preparation method of the silicon-carbon anode material according to claim 5, characterized in that, It includes at least one of the following features (1) to (3): (1) The mass concentration of the phosphoric acid solution is 40 wt% - 85 wt%; (2) The soaking time of the porous carbon in the phosphoric acid solution is 0.5 - 2 h; (3) The way of the solid-liquid separation is centrifugal separation.

7. The preparation method of the silicon-carbon anode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (3): (1) The gaseous silicon source includes at least one of silane, disilane, trichlorosilane, dichlorosilane, propylsilane, trichlorosilane and silicon chloride; (2) The temperature of the silicon deposition is 400 - 500 °C, and the time of the silicon deposition is 6 - 10 h; (3) The flow rate ratio of the gaseous silicon source to the protective gas is 2 - 4:

1.

8. The preparation method of the silicon-carbon negative electrode material according to claim 3, characterized in that, It includes at least one of the following features (1) to (3): (1) The carbon coating is performed by chemical vapor deposition. Under a protective gas atmosphere, introduce a gaseous carbon source to perform carbon coating on the phosphorus-doped silicon-carbon material; (2) The gaseous carbon source includes at least one of acetylene, methane, ethane and ethylene; (3) The temperature of the carbon coating is 500 - 600 °C, and the time of the carbon coating is 1 - 3 h.

9. A negative electrode plate, characterized in that, The negative electrode sheet includes the silicon-carbon negative electrode material according to claim 1 or 2.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet according to claim 9.

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